Graphoepitaxy directed self-assembly is a potential low-cost solution for patterning via layers with pitches beyond the reach of a single optical lithographic exposure. In this process, selective control of the interfacial energy at the bottom and sidewall of the template is an important but challenging exercise. A dual brush process is implemented, in which two brushes with distinct end-groups are consecutively grafted to the prepattern to achieve fully independent modification of the bottom and sidewall surface of the template. A comprehensive study of hole pattern quality shows that using a dual brush process leads to a substantial improvement in terms of positional and dimensional variability across the process window. These findings will be useful to others who wish to manipulate polymer–surface interactions in directed self-assembly flows.

Insertion of a graphoepitaxy directed self-assembly process as a via patterning technology into integrated circuit fabrication is seriously considered for the 7-nm node and beyond. At these dimensions, a graphoepitaxy process using a cylindrical block copolymer that enables hole multiplication can alleviate costs by extending 193-nm immersion-based lithography and significantly reducing the number of masks that would be required per layer. To be considered for implementation, it needs to be proved that this approach can achieve the required pattern quality in terms of defects and variability using a representative, aperiodic design. The patterning of a via layer from an actual 7-nm node logic layout is demonstrated using immersion lithography and graphoepitaxy directed self-assembly in a fab-like environment. The performance of the process is characterized in detail on a full 300-mm wafer scale. The local variability in an edge placement error of the obtained patterns (4.0 nm 3σ for singlets) is in line with the recent results in the field and significantly less than of the prepattern (4.9 nm 3σ for singlets). In addition, it is expected that pattern quality can be further improved through an improved mask design and optical proximity correction. No major complications for insertion of the graphoepitaxy directed self-assembly into device manufacturing were observed.

Until recent years, dimensional scaling allowed for the fabrication of smaller and faster devices with increasing capacity. Currently, the limited area and the high density of the features in such devices have made self-aligned contacts/vias (SAC or SAV) a standard technique to overcome the decreasing distance between electrically functional elements in integrated circuits. In SAV schemes, the use of hard masks to define the effective transferred patterns allows for more relaxed via patterning conditions and overlay requirements. In this work, we explore a DSA-based fully self-aligned vias (FSAV) flow to further improve on traditional SAV processes. We use directed self-assembly (DSA) of block copolymers (BCP) to generate topographic features between the metal lines, which in combination with SAV, extend the benefits of this method to both X-Y directions, while maximizing the distance between the contacts and the adjacent not-connected metal lines to avoid potential shorts, as shown in Figure 1. In order to achieve this, patterned metal and/or dielectric lines are selectively functionalized using homopolymer brushes, to form a 1:1 chemical nano-pattern of specific surface energy, such that, when a BCP layer is coated and annealed on these samples, each block will align to the metal (or dielectric) lines underneath, as shown on Figure 2. We subsequently use one of the blocks as a template to generate topographic features between the metal lines. In addition, different hard masks are characterized to find the optimal material for the current scheme. Finally, we define the design rules for integration of the proposed flow into electrical devices.

Directed self-assembly (DSA) lithography poses challenges in line edge roughness (LER)/line width roughness metrology due to its self-organized and pitch-based nature. To cope with these challenges, a characterization approach with metrics and/or updates of the older ones is required. To this end, we focus on two specific challenges of DSA line patterns: (a) the large correlations between the left and right edges of a line (line wiggling) and (b) the cross-line correlations, i.e., the resemblance of wiggling fluctuations of nearby lines. The first is quantified by the line center roughness whose low-frequency part is related to the local placement errors of device structures. For the second, we introduce the c-factor correlation function, which quantifies the strength of the correlations between lines versus their horizontal distance in pitches. The proposed characterization approach is first illustrated and explained in synthesized scanning electron microscope images with full control of their dimensional and roughness parameters; it is then applied to the analysis of line/space patterns obtained with the Liu–Nealey flow (post-Polymethyl methacrylate removal and pattern transfer), revealing the effects of pattern transfer on roughness and uniformity. Finally, we calculate the c-factor function of various next-generation lithography techniques and show their distinct footprint on the extent of cross-line correlations.

In this publication the authors have investigated both theoretically and experimentally the link between line edge roughness, target noise and overlay mark fidelity. Based on previous worki , a model is presented to explain how any given edge of a printed feature could have a mean position that varies stochastically (i.e., randomly, following a normal distribution) due to lithography stochastic variation. The amount of variation is a function of the magnitude of the LER (more accurately, all the statistical properties of the LER) and the length of the feature edge. These quantities have been analytically linked to provide an estimate for the minimum line length for both optical and e-beam based overlay metrology. The model results have been compared with experimental results from wafers manufactured at IMEC on both EUV and ArF lithographic processes developed for the 10 nm node, with extrapolation to the 5 nm node.

Grapho-epitaxy directed self-assembly is a potential low-cost solution for patterning via layers with pitches beyond the reach of a single optical lithographic exposure. In this process, selective control of the interfacial energy at the bottom and sidewall of the template is an important but challenging exercise. In this work, a dual brush process is implemented, in which two brushes with distinct end-groups are consecutively grafted to the pre-pattern to achieve fully independent modification of the bottom and sidewall surface of the template. A comprehensive study of hole pattern quality shows that using a dual brush process leads to a substantial improvement in terms of positional and dimensional variability across the process window. These findings will be useful to others who wish to manipulate polymer-surface interactions in directed self-assembly flows.

Major advancements in the directed self-assembly (DSA) of block copolymers have shown the technique’s strong potential for via layer patterning in advanced technology nodes. Molecular scale pattern precision along with low cost processing promotes DSA technology as a great candidate for complementing conventional photolithography. Our studies show that decomposition of via layers with 193-nm immersion lithography in realistic circuits below the 7-nm node would require a prohibitive number of multiple patterning steps. The grouping of vias through templated DSA can resolve local conflicts in high density areas, limiting the number of required masks, and thus cutting a great deal of the associated costs. A design method for DSA via patterning in sub-7-nm nodes is discussed. We present options to expand the list of usable DSA templates and we formulate cost functions and algorithms for the optimal DSA-aware via layout decomposition. The proposed method works a posteriori, after place-and-route, allowing for fast practical implementation. We tested this method on a fully routed 32-bit processor designed for sub-7 nm technology nodes. Our results demonstrate a reduction of up to four lithography masks when compared to conventional non-DSA-aware decomposition.

The use of directed self-assembly (DSA) of cylinder forming block copolymers (BCP) for contact hole shrink applications has gained increased attention due to the dimensions that can be achieved with this materials. Recent work has focused on engineering the dimensions and surface energy of the templates to obtain straight profiles of the cylinders assembled in them. However, the impact of process optimization on defect formation is measured using scanning electron microscopy before and after transferring the BCP features to a hardmask, which provides limited information about the presence of defects or three-dimensional morphologies in the polymer structures. To identify the presence of single defects in arrays of various densities and sizes, we use Kelvin and chain structures available in the IMEC 28-nm node via chain electrical test vehicle, Everest, in combination with templated DSA. We tuned the surface energy and dimensions of the templates with the use of random copolymers and through the exposure conditions, respectively. Finally, the contact holes obtained with templated DSA of BCP were subsequently transferred into a relevant stack to apply advanced metallization processes and, ultimately, validated electrically.

Directed self-assembly (DSA) of block copolymers (BCP) is considered a promising patterning approach for the 7-nm node and beyond. Specifically, a graphoepitaxy process using a cylindrical phase BCP may offer an efficient solution for patterning randomly distributed contact holes with subresolution pitches, such as found in via and cut mask levels. In any graphoepitaxy process, the pattern density impacts the template fill (local BCP thickness inside the template) and may cause defects due to over- or underfilling of the template. In order to tackle this issue thoroughly, the parameters that determine template fill and the influence of template fill on the resulting pattern should be investigated. Using three process flow variations (with different template surface energy), template fill is experimentally characterized as a function of pattern density and film thickness. The impact of these parameters on template fill is highly dependent on the process flow, and thus prepattern surface energy. Template fill has a considerable effect on the pattern transfer of the DSA contact holes into the underlying layer. Higher fill levels give rise to smaller contact holes and worse critical dimension uniformity. These results are important for DSA-aware design and show that fill is a crucial parameter in graphoepitaxy DSA.

This manuscript first presents a cost model to compare the cost of ownership of DSA and SAQP for a typical front end of line (FEoL) line patterning exercise. Then, we proceed to a feasibility study of using a vertical furnace to batch anneal the block co-polymer for DSA applications. We show that the defect performance of such a batch anneal process is comparable to the process of record anneal methods. This helps in increasing the cost benefit for DSA compared to the conventional multiple patterning approaches.

Directed Self Assembly (DSA) has gained increased momentum in recent years as a cost-effective means for extending lithography to sub-30nm pitch, primarily presenting itself as an alternative to mainstream 193i pitch division approaches such as SADP and SAQP. Towards these goals, IMEC has excelled at understanding and implementing directed self-assembly based on PS-b-PMMA block co-polymers (BCPs) using LiNe flow [1]. These efforts increase the understanding of how block copolymers might be implemented as part of HVM compatible DSA integration schemes. In recent contributions, we have proposed and successfully demonstrated two state-of-the-art CMOS process flows which employed DSA based on the PS-b-PMMA, LiNe flow at IMEC (pitch = 28 nm) to form FinFET arrays via both a ‘cut-last’ and ‘cut-first’ approach [2-4]. Therein, we described the relevant film stacks (hard mask and STI stacks) to achieve robust patterning and pattern transfer into IMEC’s FEOL device film stacks. We also described some of the pattern placement and overlay challenges associated with these two strategies. In this contribution, we will present materials and processes for FinFET patterning and integration towards sub-20 nm pitch technology nodes. This presents a noteworthy challenge for DSA using BCPs as the ultimate resolution for PS-b-PMMA may not achieve such dimensions. The emphasis will continue to be towards patterning approaches, wafer alignment strategies, the effects of DSA processing on wafer alignment and overlay.

Directed self-assembly of block copolymers is a promising candidate to address grand challenges towards new generations of low-cost, high-resolution nanopatterning technology. Over the past decade, poly(styrene-b-methyl methacrylate) (PS-b-PMMA) has been the most popular block copolymer applied in this area. However, further scaling towards pitches below 20 nm is hindered by its relatively low segregation strength between constituent blocks, characterized by a low Flory-Huggins interaction parameter, χ (~ 0.038 at r.t). To reach sub-10 nm feature dimensions, many high- χ block copolymer materials and processes are currently being studied. Here we investigate the DSA of PSb- PMMA with blended ionic liquid (IL) on chemically-patterned substrates via thermal annealing with a free surface. In this materials system, by adding low volume fraction of IL, a substantially higher χ than the pure block copolymer is achieved with manageable change in surface and interfacial properties so that poly(styrene-random-methyl methacrylate) brushes may be used to control substrate wetting behavior, and the blend could be assembled using thermal annealing with a free surface. In other words, PS-b-PMMA/IL may serve as a high- χ drop-in replacement for PS-b-PMMA. In this work, we provide key DSA results to determine if PS-b-PMMA/IL blends would offer a solution for sub-10 nm lithography.

Directed self-assembly (DSA) of block copolymers (BCP) is considered a promising patterning approach for the 7 nm node and beyond. Specifically, a grapho-epitaxy process using a cylindrical phase BCP may offer an efficient solution for patterning randomly distributed contact holes with sub-resolution pitches, such as found in via and cut mask levels. In any grapho-epitaxy process, the pattern density impacts the template fill (local BCP thickness inside the template) and may cause defects due to respectively over- or underfilling of the template. In order to tackle this issue thoroughly, the parameters that determine template fill and the influence of template fill on the resulting pattern should be investigated. In this work, using three process flow variations (with different template surface energy), template fill is experimentally characterized as a function of pattern density and film thickness. The impact of these parameters on template fill is highly dependent on the process flow, and thus pre-pattern surface energy. Template fill has a considerable effect on the pattern transfer of the DSA contact holes into the underlying layer. Higher fill levels give rise to smaller contact holes and worse critical dimension uniformity. These results are important towards DSA-aware design and show that fill is a crucial parameter in grapho-epitaxy DSA.

DSA lithography poses new challenges in LER/LWR metrology due to its self-organized and pitch-based nature. To cope with these challenges, a novel characterization approach with new metrics and updating the older ones is required. To this end, we focus on two specific challenges of DSA line patterns: a) the large correlations between the left and right edges of a line (line wiggling, rms(LWR)<rms(LER)) and b) the cross-line correlations, i.e. the resemblance of wiggling fluctuations of nearby lines. The first is quantified by the Line Center Roughness whose low-frequency part is related to the local placement errors of device structures. For the second, we propose the c-factor correlation function which quantifies the strength of the correlations between lines versus their horizontal distance in pitches. Also, we define roughness and uniformity parameters for the pitch changes along and across lines. The proposed characterization approach is applied to the analysis of line/space patterns obtained with the Liu-Nealey (LiNe) flow (post PMMA removal and pattern transfer) revealing the effects of pattern transfer on roughness and uniformity. Finally, we calculate the cfactor function of various Next-Generation Lithography techniques and reveal their distinct footprint on the extent of cross-line correlations.

The dimensional scaling in IC manufacturing strongly drives the demands on CD and defect metrology techniques and their measurement uncertainties. Defect review has become as important as CD metrology and both of them create a new metrology paradigm because it creates a completely new need for flexible, robust and scalable metrology software. Current, software architectures and metrology algorithms are performant but it must be pushed to another higher level in order to follow roadmap speed and requirements. For example: manage defect and CD in one step algorithm, customize algorithms and outputs features for each R&D team environment, provide software update every day or every week for R&D teams in order to explore easily various development strategies. The final goal is to avoid spending hours and days to manually tune algorithm to analyze metrology data and to allow R&D teams to stay focus on their expertise. The benefits are drastic costs reduction, more efficient R&D team and better process quality.

In this paper, we propose a new generation of software platform and development infrastructure which can integrate specific metrology business modules. For example, we will show the integration of a chemistry module dedicated to electronics materials like Direct Self Assembly features. We will show a new generation of image analysis algorithms which are able to manage at the same time defect rates, images classifications, CD and roughness measurements with high throughput performances in order to be compatible with HVM. In a second part, we will assess the reliability, the customization of algorithm and the software platform capabilities to follow new specific semiconductor metrology software requirements: flexibility, robustness, high throughput and scalability. Finally, we will demonstrate how such environment has allowed a drastic reduction of data analysis cycle time.

This manuscript shows the relationship between defectivity of a typical chemo-epitaxy sequence and the DSA-specific materials, namely the mat, the brush and the block co-polymer. We demonstrate that the density of assembly defects in a line-space DSA flow, namely the dislocations and 1-period bridges have a direct correlation to certain parameters in the synthesis sequence of these materials. The primary focus of this manuscript is on identifying, controlling and reproducing the defects-critical parameters in the block co-polymer synthesis process for a stable and low defect performance of DSA flows.

Directed self-assembly (DSA) of block copolymers (BCP) has attracted significant interest as a patterning technique over the past few years. We have previously reported the development of a new process flow, the CHIPS flow (Chemo-epitaxy Induced by Pillar Structures), where we use ArFi lithography and plasma etch to print guiding pillar patterns for the DSA of cylindrical phase BCPs into dense hexagonal hole arrays of 22.5 nm half-pitch and 15 nm half-pitch [1]. The ability of this DSA process to generate dense regular patterns makes it an excellent candidate for patterning memory devices. Thus, in this paper we study the applicability of the CHIPS flow to patterning for DRAM storage layers. We report the impact of various process conditions on defect density, defect types and pattern variability. We also perform detailed analysis of the DSA patterns, quantify pattern placement accuracy and demonstrate a route towards excellent LCDU after pattern transfer into a hard mask layer.

In this paper, approaches are explored for combining EUV with DSA for via layer patterning at the N7 and N5 logic nodes. Simulations indicate opportunity for significant LCDU improvement at the N7 node without impacting the required exposure dose. A templated DSA process based on NXE:3300 exposed EUV pre-patterns has been developed and supports the simulations. The main point of improvement concerns pattern placement accuracy with this process. It is described how metrology contributes to the measured placement error numbers. Further optimization of metrology methods for determining local placement errors is required. Next, also via layer patterning at the N5 logic node is considered. On top of LCDU improvement, the combination of EUV with DSA also allows for maintaining a single mask solution at this technology node, due to the ability of the DSA process to repair merging vias. It is experimentally shown, how shaping of templates for such via multiplication helps in placement accuracy control. Peanut-shaped pre-patterns, which can be printed using EUV lithography, give significantly better placement accuracy control compared to elliptical pre-patterns.

In recent years, major advancements have been made in the directed self-assembly (DSA) of block copolymers (BCPs). As a result, the insertion of DSA for IC fabrication is being actively considered for the sub-7nm nodes. At these nodes the DSA technology could alleviate costs for multiple patterning and limit the number of litho masks that would be required per metal layer. One of the most straightforward approaches for DSA implementation would be for via patterning through templated DSA, where hole patterns are readily accessible through templated confinement of cylindrical phase BCP materials.

Our in-house studies show that decomposition of via layers in realistic circuits below the 7nm node would require at least many multi-patterning steps (or colors), using 193nm immersion lithography. Even the use of EUV might require double patterning in these dimensions, since the minimum via distance would be smaller than EUV resolution. The grouping of vias through templated DSA can resolve local conflicts in high density areas. This way, the number of required colors can be significantly reduced.

For the implementation of this approach, a DSA-aware mask decomposition is required. In this paper, our design approach for DSA via patterning in sub-7nm nodes is discussed. We propose options to expand the list of DSA-compatible via patterns (DSA letters) and we define matching cost formulas for the optimal DSA-aware layout decomposition. The flowchart of our proposed approach tool is presented.

In recent years, major advancements have been made in the directed self-assembly (DSA) of block copolymers (BCP). Insertion of DSA for IC fabrication is seriously considered for the 7 nm node. At this node the DSA technology could alleviate costs for multiple patterning and limit the number of masks that would be required per layer. At imec, multiple approaches for inserting DSA into the 7 nm node are considered. One of the most straightforward approaches for implementation would be for via patterning through templated DSA; a grapho-epitaxy flow using cylindrical phase BCP material resulting in contact hole multiplication within a litho-defined pre-pattern. To be implemented for 7 nm node via patterning, not only the appropriate process flow needs to be available, but also DSA-aware mask decomposition is required. In this paper, several aspects of the imec approach for implementing templated DSA will be discussed, including experimental demonstration of density effect mitigation, DSA hole pattern transfer and double DSA patterning, creation of a compact DSA model. Using an actual 7 nm node logic layout, we derive DSA-friendly design rules in a logical way from a lithographer’s view point. A concrete assessment is provided on how DSA-friendly design could potentially reduce the number of Via masks for a place-and-routed N7 logic pattern.

High-defect density in thermodynamics driven directed self-assembly (DSA) flows has been a major cause of concern for a while and several questions have been raised about the relevance of DSA in high-volume manufacturing. The major questions raised in this regard are: (1) What is the intrinsic level of DSA-induced defects? (2) Can we isolate the DSA-induced defects from the other processes-induced defects? (3) How much do the DSA materials contribute to the final defectivity and can this be controlled? (4) How can we understand the root causes of the DSA-induced defects and their kinetics of annihilation? (5) Can we have block copolymer anneal durations that are compatible with standard CMOS fabrication techniques (in the range of minutes) with low-defect levels? We address these important questions and identify the issues and the level of control needed to achieve a stable DSA defect performance.

Directed self-assembly of block copolymers over chemically patterned substrates has proven to be an effective method for sublithographic patterning. Features on these chemical patterns can be multiplied by the natural domain-spacing of the block copolymer assembled on top of the substrate through pattern interpolation. The LiuNealey (LiNe) chemoepitaxy flow for directed self-assembly allows for modification of the geometry and chemistry of the nanopatterned substrate. The critical dimensions and period along with the chemical composition of the patterned features in the LiNe flow govern the equilibrium morphology of the assembled block copolymer. We demonstrate how the construction of the chemical pattern affects the selection for desired, well-registered assembly of block copolymer melts by using a theoretically informed coarse-grained many-body model of block copolymers. The molecular simulations are used to provide an explanation for how to best design the chemical pattern in the LiNe flow for the directed self-assembly (DSA) of block copolymers to achieve desired line-andspace structures.

Directed Self-Assembly (DSA) of block copolymers (BCP) has attracted increasing attention as the potential next generation lithography technology. One of the most promising applications of DSA is the patterning of contact holes in IC circuits using physical guiding templates. In previous studies, researchers have demonstrated that DSA patterns are determined not only by the size and shape of guiding templates, but the template density as well. However, the influence of the pattern density has not been explored systematically, nor is there a fast inspection methodology to visualize and quantify the influence. In this paper, we introduce the concept of DSA Interaction Range (DSAIR). The influence of template density on the DSA patterns is examined using Gaussian convolution of x with y [say what it is a convolution of]. This approach provides us with a fast and quantitative way to model the influence of template density and predict the location of overfilled conditions.

Directed Self Assembly (DSA) processes offer the promise of providing alternative ways to extend optical lithography cost-effectively for sub-10nm nodes and present itself as an alternative pitch division approach. As a result, DSA has gained increased momentum in recent years, as a means for extending optical lithography past its current limits. The availability of a DSA processing line can enable to further push the limits of 193nm immersion lithography and overcome some of the critical concerns for EUV lithography.

Numerous block copolymer (BCP) systems can be used in directed self-assembly (DSA) processes to form patterns useful in lithography, especially lines and spaces with lamellar phase systems and vias/pillars with cylindrical phase systems. However, most of these BCP systems with attractive pattern formation capabilities have limited plasma etch contrast between the polymer domains. One potential solution to greatly enhance this etch contrast is a recently developed technique called sequential infiltration synthesis (SIS). SIS is a self-limiting synthesis technique, like atomic layer deposition, where organometallic (OM) precursor vapours and oxidants are introduced into self-assembled block copolymer systems in multiple cycles. In the first half of each cycle the OM precursor selectively reacts with one polymer domain, and in the second half of the cycle the oxidant reacts with the OM groups in the polymer film to selectively form metallic compounds in one of the polymer domains. Thus, the polymer pattern is transformed into a metallic mask with much enhanced plasma etch contrast. We report the effects of such a block-selective SIS process of metallic compounds on the feature sizes, roughness and profiles of patterns formed with BCP systems.

Directed Self-Assembly (DSA) is one of the leading candidates for next generation patterning in IC manufacturing. With the continued delay of EUV and the increasing costs of evermore complex multipatterning techniques, DSA has the potential to produce small, well-defined features on a tight pitch. The graphoepitaxy DSA approach can be used to form single or multiple uniform contact holes (cylinders) well below the resolution limit of the optical exposure tool in a pre-pattern template. The utility of these patterns in the semiconductor manufacturing process is dependent on the capability of the process to control the size, edge roughness and placement of these DSA structures in the presence of reasonable levels of variation in the DSA material, the processing of that material and the pre-pattern template. In this study, a 3-D Self-Consistent Field Theory (SCFT) model has been developed to describe the behavior of such DSA systems. The utility of the simulator to describe actual physical behavior is explored, by fine tuning the SCFT model input parameters against experimental data for certain pre-pattern configurations and then evaluating the model predictions for other separate pre-pattern shapes. Two separate calibration studies are presented, one with 2-D guide patterns, in which multiple holes are positioned in a 2-D irregular array, and the other with 1-D structures, where the holes are distributed along one direction only. Pattern contours are extracted from CD-SEM images. A metric that measures the CD and placement is used to evaluate the modeled contours against the experimental contours.

The patterning potential of block copolymer (BCP) materials via various directed self-assembly (DSA) schemes has been demonstrated for over a decade. We have previously reported the HONEYCOMB flow; a process flow where we utilize Extreme Ultraviolet Lithography and Oxygen plasma to guide the assembly of cylindrical phase BCPs into regular hexagonal arrays of contact holes [1, 2]. In this work we report the development of a new process flow, the CHIPS flow, where we use ArFi lithography to print guiding patterns for the chemo-epitaxial DSA of BCPs. Using this process flow we demonstrate BCP assembly into hexagonal arrays with sub-25 nm half-pitch and discuss critical steps of the process flow. Additionally, we discuss the influence of under-layer surface energy on the DSA process window and report contact hole metrology results.

Directed self-assembly (DSA) of block copolymers (BCP) is attracting a growing amount of interest as a technique to expand traditional lithography beyond its current limits. It has recently been demonstrated that chemoepitaxy can be used to successfully direct BCP assembly to form large arrays of high-density features using the ‘LiNe’ flow. This process uses lithography and trim-etch to produce a “prepattern” of stripes of alternating chemical composition, which in turn guide the formation of assembled BCP structures. The entire process is predicated on the preferential interaction of the respective BCP domains with particular regions of the underlying prepattern. The natural and relative strength of these interactions are at least partially responsible for many aspects of the resulting assembled BCP film, including equilibrium morphology, type and persistence of kinetically trapped defects, and domain roughness. This study develops the understanding of how various guiding chemistries ultimately govern BCP morphology and characteristics in the LiNe flow. In particular, the work focuses on how stronger affinity between chemical patterns and the guided BCP film leads to faster assembly, lower ultimate defectivity levels, and better incommensurability tolerance, as well as the relationship between pattern strength and domain roughness. One issue in generating finely controllable chemical patterns is that all materials are affected to some degree by processing, which can modify or weaken the guiding ability of the pattern. This investigation addresses the non-idealities introduced in production processing and explores how this knowledge can be employed in improving BCP DSA for lithography.

Cylindrical directed self-assembly (DSA) nanostructures is a promising candidate for patterning the contacts and vias in integrated circuits. To match the contact patterns in an IC layout, physical guiding templates have been adopted to generate aperiodic DSA patterns, and templates of different sizes could lead to various DSA patterns. It is found in the experiment that the density of guiding templates has a strong influence on the DSA patterns. At a low template density, templates tend to become overfilled and result in DSA defects. In this paper, we experimentally demonstrate an effective solution to counteract the influence of template pattern density on the quality of DSA using sub-DSA-resolution Assist Features (SDRAFs). We show that SDRAFs can reduce the DSA defects significantly.

High defect density in thermodynamics driven DSA flows has been a major cause of concern for a while and several questions have been raised about the relevance of DSA in high volume manufacturing. The major questions raised in this regard are: 1. What is the intrinsic level of DSA-induced defects, 2. Can we isolate the DSA-induced defects from the other processes-induced defects, 3. How much do the DSA materials contribute to the final defectivity and can this be controlled, 4. How can we understand the root causes of the DSA-induced defects, their kinetics of annihilation and finally, 5. Can we have block co-polymer anneal durations that are compatible with standard CMOS fabrication techniques (in the range of minutes) with low defect levels. This manuscript addresses these important questions and identifies the issues and the level of control needed to achieve a stable DSA defect performance.

Directed self-assembly (DSA) of lamellae-forming block copolymers (BCP) via chemo-epitaxy is a potential lithographic solution to achieve patterns of dense features. Progress to date demonstrates encouraging results, but in order to better understand the role of all parameters, systematic analysis of each factor needs to be assessed. Small changes in the volume fraction of a lamellae-forming BCP have been shown to change the connectivity of unguided domains. When an asymmetric lamellae-forming BCP is assembled on chemical patterns generated with the LiNe flow, the patterning performance and defect modes change depending on whether the majority or minority volume fraction phase is guided by the chemical pattern. Asymmetric BCP formulations were generated by blending homopolymer with a symmetric BCP. The patterning performance of the BCP formulations was assessed for different pattern pitches, guide stripe widths, backfill materials and annealing times. Optical defect inspection and SEM review are used to track the majority defect mode for each formulation. Formulation-dependent trends in defect modes show the importance of optimizing the BCP formulation in order to minimize the defectivity.

In recent years major advancements have been made in the directed self-assembly (DSA) of block copolymers (BCP). Insertion of DSA for IC fabrication is seriously considered for the 7nm node. At this node the DSA technology could alleviate costs for double patterning and limit the number of masks that would be required per layer. At imec multiple approaches for inserting DSA into the 7nm node are considered. One of the most straightforward approaches for implementation would be for via patterning through templated DSA (grapho-epitaxy), since hole patterns are readily accessible through templated hole patterning of cylindrical phase BCP materials. Here, the pre-pattern template is first patterned into a spin-on hardmask stack. After optimizing the surface properties of the template the desired hole patterns can be obtained by the BCP DSA process. For implementation of this approach to be implemented for 7nm node via patterning, not only the appropriate process flow needs to be available, but also appropriate metrology (including for pattern placement accuracy) and DSA-aware mask decomposition are required. In this paper the imec approach for 7nm node via patterning will be discussed.

In this paper we address an important topic for the development of block copolymer directed self assembly, which is the lack of the third dimensional information. The three-dimensional shape of the DSA feature directly impacts the ability to transfer the DSA pattern into etched patterns. Through TEM sample preparation by in-situ focused ion beam (FIB) Pt deposition and milling, we show cross-sectional images for the two most elemental building blocks of directed self assembled block copolymers, namely, the single and double-hole (peanut shape) etched in Si structures with great contrast at the interface formed by PS and PMMA. Additionally, a hard-mask single hole structure processed with a different template material is shown as well. Elemental mapping with energy filtered TEM (EFTEM) was shown to assist interpretation of images. 3D reconstruction of the holes formed in the hard-mask sample was performed using dark field (DF) STEM. A reduction in the SOC and SOG thickness was observed post in-situ Pt deposition for the hard mask structure. Further TEM sample preparation improvements will be needed to minimize the compression observed.

Grazing-Incidence Small Angle X-ray Scattering (GISAXS) offers the ability to probe large sample areas, providing three-dimensional structural information at high detail in a thin film geometry. In this study we exploit the application of GISAXS to structures formed at one step of the LiNe (Liu-Nealey) flow using chemical patterns for directed self-assembly of block copolymer films. Experiments conducted at the Argonne National Laboratory provided scattering patterns probing film characteristics at both parallel and normal directions to the surface. We demonstrate the application of new computational methods to construct models based on scattering measured. Such analysis allows for extraction of structural characteristics at unprecedented detail.

Directed Self Assembly (DSA) of Block Co-Polymers (BCP) has become an intense field of study as a potential patterning solution for future generation devices. The most critical challenges that need to be understood and controlled include pattern placement accuracy, achieving low defectivity in DSA patterns and how to implement this process as a patterning solution. The DSA program at imec includes efforts on these three major topics. Specifically, in this paper the progress for the templated DSA flow within the imec program will be discussed. An experimental assessment is made based on a 37 nm BCP pitch material. In particular, the impact of different process options is illustrated, and data for CD and placement accuracy of the DSA holes in their template is provided.

Significant interest from the integrated circuit (IC) industry has been placed on directed selfassembly (DSA) for sub 10nm nodes. DSA is being considered as a cost reduction complementary process to multiple patterning (MP) and an enabler of new technology nodes. However, to realize the potential of this technology, it is essential to look holistically at the necessary infrastructure from the point of view of materials, hardware, software, process integration and design methodologies which enable its deployment in large volume manufacturing. One key aspect in enabling DSA processes is the ability to mirror functionality of full chip mask synthesis and verification methods of existing tools used in production. One of those critical components is the ability to accurately model the placement of the target phases in the DSA process with a given mask shape, as well as determining the conditions at which unwanted phase transitions start to occur. Self-consistent field theory and Monte Carlo1 simulators have the capability to probe and explore the mechanisms driving the different phases of a diblock copolymer system. While such methods are appropriate to study the nature of the self-assembly process, they are computationally expensive and they cannot be used to perform mask synthesis operations nor full chip verification. The nature of a compact model is to make a series of approximations allowing a simpler description of the problem in a way that the phenomena of interest can be sufficiently captured even if it is at the expense of its generality. In this case we focus our effort in establishing the minimum set of conditions that a compact model for the manufacture of contact holes using a grapho epitaxy process for a PS-PMMA diblock copolymer system needs. The processes uses etched short trenches as guiding patterns in which the vertical DSA cylinders are formed. By focusing in the phase of interest (i.e., cylinder forming conditions), it is possible to reformulate the problem in a phenomenological formulation which accounts for the interaction among cylinders, the volume fraction of the respective co-polymers and the interaction with the confinement walls. As such, a 2D approximation to the 3D environment can be applied too simplify thhe representation of the DSA process. This enables thee use of a 2D contour for compact model training and verification. Further simplification is not recommended due to the nature of the grapho-epitaxy guiding patterns, where a simple CD measurement is not sufficient to capture the 2D environment of post routed contact patterns for sub 10nm nodes. In this paper, we will study the application of the DSA compact model to a via layer of imec’s 7nm technology node standard cells. ArF immersion lithography will be used to pattern the guides, and the layout will be DSA compliant to determine the mask complexity as well as the sensitivity of the solution to mask biases for the contact layer.

EUV photoresists are considered as a potential source of optics contamination, since they introduce irradiation-induced outgassing in the EUV vacuum environment. Therefore, before these resists can be used on e.g. ASML NXE:3100 or NXE:3300, they need to be tested in dedicated equipment according to a well-defined procedure, which is based on exposing a witness sample (WS) in the vicinity of a simultaneously exposed resist as it outgasses. Different system infrastructures are used at multiple sites (e.g. NIST, CNSE, Sematech, EIDEC, and imec) and were calibrated to each other by a detailed test plan. Despite this detailed tool qualifications, a first round robin comparison of identical materials showed inconsistent outgas test results, and required further investigation by a second round robin. Since the resist exposure mode is different at the various locations (some sites are using EUV photons while others use E-gun electrons), this difference has always a point of concern for variability of test results. In this work we compare the outgas test results from EUV photon and electron exposure using the resist materials of the second round robin. Since the imec outgas tester allows both exposure methods on the resist, a within-system comparison is possible and showed limited variation between photon and electron exposure mode. Therefore the system-to-system variability amongst the different outgas test sites is expected to be related to other parameters than the electron/photon exposure mode. Initial work showed that the variability might be related to temperature, E-gun emission excursion, and/or residual outgassing scaled by different wafer areas at the different sites.

Directed self-assembly (DSA) is being actively investigated as a potential patterning solution for future generation devices. While SEM based CD measurement is currently used in research and development, scatterometry-based techniques like spectroscopic CD (SCD) are preferred for high volume manufacturing. SCD can offer information about sub-surface features that are not available from CD-SEM measurement. Besides, SCD is a non-destructive, high throughput technique already adopted in HVM in several advanced nodes. The directed self assembly CD measurement can be challenging because of small dimensions and extremely thin layers in the DSA stack. In this study, the SCD technology was investigated for a 14 nm resolution PS-b-PMMA chemical epitaxy UW process optimized by imec. The DSA stack involves new materials such as cross-linkable polysterene (XPS) of thickness approximately 5 nm, ArF immersion resist (subsequently removed), -OH terminated neutral brush layer, and BCP material (Polystyrene-blockmethyl methacrylate of thickness roughly 20 to 30 nm). The mask contains a large CD and pitch matrix, for studying the quality of self-assembly as a function of the guide pattern dimensions. We report on the ability of SCD to characterize the dimensional variation in these targets and hence provide a viable process control solution.

An electrical test vehicle for fabricating direct self-assembly (DSA) sub-30 nm via interconnects has been fabricated employing a soft mask grapho-epitaxy contact-hole shrink. The generation of the resist pre-pattern was carried out using 193i lithography on three different stacks and the BCP assembly was evaluated with and without template affinity control on the resist pre-pattern. After DSA shrink, the holes were transferred in a 100 nm oxide for standard Tungsten metallization for electrical characterization.

The patterning potential of block copolymer materials via various directed self-assembly (DSA) schemes has been demonstrated for over a decade. At cost-effective low printing doses, extreme ultra-violet lithography (EUVL) suffers from shot noise effects while patterning sub 30 nm contact hole dimensions. As the critical dimension (CD) of DSA systems is largely determined by polymer dimensions, it is theoretically expected that the local CD uniformity (LCDU) of EUVL pre-patterns can be improved by the DSA of pitch matched block co-polymers. In this work we demonstrate continued improvements on our previously reported chemo-epitaxy DSA integration flow. Also, we achieve dense arrays of contact holes via 3x and 4x frequency multiplication of EUVL patterned contact hole arrays.

Directed Self-Assembly (DSA) of Block Co-Polymers (BCP) has become an intense field of study as a potential patterning solution for future generation devices. The most critical challenges that need to be understood and controlled include pattern placement accuracy, achieving low defectivity in DSA patterns and how to make chip designs DSA-friendly. The DSA program at imec includes efforts on these three major topics. Specifically, in this paper the progress in DSA defectivity within the imec program will be discussed. In previous work, defectivity levels of ~560 defects/cm2 were reported and the root causes for these defects were identified, which included particle sources, material interactions and pre-pattern imperfections. The specific efforts that have been undertaken to reduce defectivity in the line/space chemoepitaxy DSA flow that is used for the imec defectivity studies are discussed. Specifically, control of neutral layer material and improved filtration during the block co-polymer manufacturing have enabled a significant reduction in the defect performance. In parallel, efforts have been ongoing to enhance the defect inspection capabilities and allow a high capture rate of the small defects. It is demonstrated that transfer of the polystyrene patterns into the underlying substrate is critical for detecting the DSA-relevant defect modes including microbridges and small dislocations. Such pattern transfer enhances the inspection sensitivity by ~10x. Further improvement through process optimization allows for substantial defectivity reduction.

Directed self-assembly (DSA) of block copolymers (BCP) via chemo-epitaxy is a potential lithographic solution to
patterns of dense features. The LiNe (Liu-Nealey) flow was used to fabricate the chemical pattern, which guides the BCP
due to the different wetting behavior of the materials. Fine control of both the chemical pattern chemistry and geometry
are important for DSA of BCP. Furthermore, wetting behavior considerations for DSA extend beyond pattern design and
include the surrounding region. BCP DSA would be easier to integrate into device design if the patterned region were
isolated with a featureless region (horizontal lamellar BCP assembly) rather than undirected BCP fingerprint structures.
This paper addresses two processing steps found to be modifying the guide material. For one, the backfill brush grafts to
the cross-linked polystyrene (XPS), albeit at a lower rate than the brush grafts to the exposed substrate. Undersaturating
the backfill brush only moderately improves the XPS wetting behavior, but also negatively impacts the background
region of the chemical pattern. Replacing the brush grafting functionality so that the brush grafts at lower annealing
conditions also did not avoid the side reaction between the brush and the XPS. The other step modifying the XPS is the
trim etch. Replacing the trim etch process was effective at generating a chemical pattern that can orient the BCP
horizontally on a stripe 11 L0 wide passing through a field of chemical pattern.

Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the
most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA
patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the
DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of
other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.),
the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces
very little defect scattering signal. These defects, termed as “dislocation” and “disclination” have unique shapes and have
very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and
disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a
silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous
Coupled-Wave Analysis (RCWA) method for solving Maxwell’s equations to simulate the DSA unique defects and
calculate inspection parameters. Controllable inspection parameters include various illumination and collection
apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA
simulation, we compared SNR between “Post-SiN etch” and “Post-SiN+Si-substrate etch” steps. The study is also
extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed
dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA
unique defect types.

Directed self-assembly (DDSA) of block copolymers ((BCP) is attracting a growing amount of interest as a techhnique to expand traditional lithography beyond its current limits. It has reecently been demonstrated that chemoepitaxy can be used to successfully ddirect BCP assembly to form large arrays off high-density features. The imec DSA LiNe flow uses lithography and trim-etch to produce a “prepattern” of cross-linked polystyrene (PS) stripes, which in turn guide the formation of assembled BCPP structures. Thhe entire process is predicated on the preferential interaction of the respective BCP domains with particular regionss of the underlying prepattern. The use of polystyrene as the guiding material is not uniquely required, however, and in fact may not even be preferable. This study investigates an alternate chemistry –– crosslinked poly(methyl methacrylate), X-PMMA, –– as the underlying polymer mat, providing a route to higher auto-affinity and therefore a stronger guiding ability. In addition to tthe advantages of the chemistry under investigation, this study explores the broader theme of extending BCP DSA to other materials.

Resolution requirements for photolithography have reached beyond the wavelength of light.
Consequently, it is becoming increasingly complicated and expensive to further minimize feature
dimensions as required to push the limits of Moore’s law. EUV lithography has been the much
anticipated solution; however, its insertion timing for High Volume Manufacturing is still an uncertainty
due to source power and EUV mask infrastructure limitations.
Extending the limits of 193nm immersion lithography requires pitch division using either Double
Patterning Pitch Division (DPPD), and/or Spacer Based Pitch Division (SBPD) schemes (e.g. Hard mask
image transfer methods (Double, Triple, Quadruple)). While these approaches reduce pitch, there is an
associated risk/compromise of process complexity, and overlay accuracy budget issues.
Directed Self Assembly (DSA) processes offer the promise of providing alternative ways to extend optical
lithography cost-effectively for sub-10nm nodes and present itself as an alternative pitch division
approach. As a result, DSA has gained increased momentum in recent years, as a means for extending
optical lithography past its current limits. The availability of a DSA processing line can enable to further
push the limits of 193nm immersion lithography and overcome some of the critical concerns for EUV
lithography.
Robust etch transfer of DSA patterns into commonly used device integration materials such as silicon,
silicon nitride, and silicon dioxide had been previously demonstrated [1,2]. However DSA integration to
CMOS process flows, including cut/keep structures to form fin arrays, is yet to be demonstrated on
relevant film stacks (front-end-of-line device integration such as hard mask stacks, and STI stacks). Such
a demonstration will confirm and reinforce its viability as a candidate for sub-10nm technology nodes.

Directed Self-Assembly (DSA) of Block Co-Polymers (BCP) has become an intense field of study as a potential patterning
solution for future generation devices. The most critical challenges that need to be understood and controlled include
pattern placement accuracy, achieving low defectivity in DSA patterns and how to make chip designs DSA-friendly. The
DSA program at imec includes efforts on these three major topics. Specifically, in this paper the progress in setting up
flows for templated DSA within the imec program will be discussed. A process has been implemented based on a hard
mask as the template layer. In this paper primarily the impact of local pattern density and BCP film thickness on the
templated DSA process are discussed. The open hole rate and the placement accuracy of BCP patterns within the template
are the primary figures of merit.

As design rule shrinks, it is essential that the capability to detect smaller and smaller defects should improve. There is considerable effort going on in the industry to enhance immersion lithography using directed self-assembly (DSA) for the 14-nm design node and below. While the process feasibility is demonstrated with DSA, material issues as well as process control requirements are not fully characterized. The chemical epitaxy process is currently the most-preferred process option for frequency multiplication, and it involves new materials at extremely small thicknesses. The image contrast of the lamellar line/space pattern at such small layer thicknesses is a new challenge for optical inspection tools. The study focuses on capability of optical inspection systems to capture DSA unique defects such as dislocations and disclination clusters over the system and wafer noise. The study is also extended to investigate wafer-level data at multiple process steps and to determine the contribution from each process step and materials using defect source analysis methodology. The added defect pareto and spatial distributions of added defects at each process step are discussed.

One of the main challenges for developing extreme ultraviolet resists is to satisfy critical dimension uniformity (CDU) and sidewall roughness of contacts to the allowable limit. To this end, further understanding of the effects of resist ingredients on CDU and contact edge roughness (CER) is required. We investigate the effects of a photoacid generator (PAG), sensitizer and quencher concentrations on the CDU and CER. We find that the dependencies of CDU on sensitizer and quencher are dominated by photon shot noise (PSN) effects whereas a more complicated interplay between PSN and PAG distribution statistics should be considered in the dependence of CDU on PAG concentration. The estimated CER parameters [root mean square (RMS) value and correlation length ξ ] exhibit a merging trend when plotted against the final critical dimension (CD). In addition, RMS value increases with exposure dose and PAG loading contrary to shot noise expectations. Power spectrum analysis reveals the dominant contribution of low-frequency undulations to CER, which is attributed to the enhanced interaction along specific directions between the aerial image and/or acid kinetics of nearby contacts. This inter-contact effect is further intensified with CD for fixed pitch and may explain the observed CER behavior.

Fingerprint edge roughness (FER) is proposed to characterize high frequency roughness of fingerprint pattern edges assembled by lamella forming block copolymer (BCP). The FER is a roughness index which does not include the roughness component of the fingerprint curvature. A technique to evaluate FER by using CD-SEM is also proposed. Centerline of the fingerprint patterns were extracted by utilizing binarization and slimming algorithm, and line width, line width roughness and line edge roughness along the centerline were measured. The FER thus measured showed a good agreement with those determined by utilizing conventional line edge roughness analyzing algorithm. The FERs of fingerprint patterns assembled with various BCP formulations were analyzed. As a result, the proposed technique successfully detected the line edge roughness difference between each BCP formulations with different compositions. The results indicate that the FER might be a useful index to evaluate the patterning performance of BCP as a material for DSA process. The proposed technique will provide a method for fast and easy development of BCP materials and processes

Process variability in today’s EUV lithography might be a showstopper for features below 27nm dimensions. At these
feature sizes, electrical devices are influenced by quantum effects and thus have to face the discrete behavior of light and matter. More in general, lithography uncertainties arise from each lithographic element: the source, the photomask, the optical system, and the photoresist. In order to individually assess all the different contributions to the final resist roughness, a EUV mask with known absorber pattern variability was used to expose different resists at different process conditions. CD-SEM analyses were performed on both mask absorber and resist pattern and then used to build a stochastic resist model. In this first paper, we present a complete characterization of the root causes which are responsible of the CD nonuniformity for 27nm half-pitch dense contact-holes exposed with the ASML NXE:3100 scanner installed at imec. Using the same stochastic model, a simulated evaluation to quantify the possible impact of the different elements composing the lithographic process is performed at higher numerical aperture.

EUV photoresists are considered as a potential source of optics contamination, since they introduce irradiation induced outgassing in the EUV vacuum environment. Therefore, before these resists can be used on e.g. ASML NXE:3100 or NXE:3300, they need to be tested in dedicated equipment according to a well-defined procedure, which is based on exposing a witness sample (WS) in the vicinity of a simultaneously exposed resist as it outgasses. Such an outgassing test infrastructure is available at many sites, but exposure modes on the witness sample and wafer can be significantly different, which potentially could lead to different test results. In this investigation, we first explored in more detail the relationship between resist outgassing as measured by RGA (Residual Gas Analysis) and the carbon growth obtained in the WS test. A good correlation was found by using a timeintegrated and mass-weighted sum of the RGA-measured mass peaks. Next, the impact of the resist exposure mode on the WS contamination result was investigated at imec, where the outgas test setup allows to expose the wafer with EUV irradiation as well as electrons in the same vacuum environment. It was found that minor differences observed in the WS test results, can be explained by adequate characterization of exposure intensity distribution and dose control. Finally the WS test results at imec from the different exposure modes were compared to the test results at NIST. The small differences in contamination that were observed could be explained by differences in test procedure, by using the time dependent RGA approach. From the combined work on outgassing measurements and WS contamination testing we have significantly improved our understanding of the relationship between outgassing and contamination processes induced by EUV photons and electrons. We have also demonstrated how to compare results obtained at different outgas testing sites, which is important in quantifying the potential risk to EUV device manufacturing posed by resist outgassing.

One critical problem with EUV patterning is the local CD variation of contact holes. The issue is especially problematic for patterning of sub-30nm hole dimensions. Although the EUV wavelength enables resolution of fine contact patterns, shot noise effects (both chemical and optical) result in high levels of CD non-uniformity. Directed self-assembly (DSA) offers the possibility of rectifying this non-uniformity. Since the resulting CD in this patterning approach is typically dictated by the polymer size, application of this technology in conjunction with an EUV-defined pre-pattern can theoretically improve the local CD uniformity. Integration approaches using both chemo- and grapho-epitaxy integration may be used to achieve DSA enabled uniformity improvement. The drawbacks and benefits of both approaches will be discussed. Finally, these types of DSA flows also enable frequency multiplication to achieve dense arrays from an initially sparse pattern. In this study, we will report on a variety of schemes to attain rectification and frequency multiplication.

Directed Self-Assembly (DSA) has become a promising alternative for generating fine lithographic patterns. Since contact holes are among the most difficult structures to resolve through traditional lithographic means, directed selfassembly applications that generate smaller contact holes are of particular interest to the industry. In this paper, DSA integrations that shrink pre-patterned contact holes were explored. The use of both block copolymers (BCPs)1 and blended polymer systems2 was considered. In addition, both wet3 and dry4 techniques were used to develop the central core out of the respective phase-separated morphologies. Finally, the hole patterns created through the various contact hole applications were transferred to substrates of interest with the goal of incorporating them into an IMEC 28 nm node via chain electrical test vehicle for direct, side-by-side comparison.

As design rule shrinks, it is essential that the capability to detect smaller and smaller defects should improve. There is
considerable effort going on in the industry to enhance Immersion Lithography using DSA for 14 nm design node and
below. While the process feasibility is demonstrated with DSA, material issues as well as process control requirements
are not fully characterized. The chemical epitaxy process is currently the most-preferred process option for frequency
multiplication and it involves new materials at extremely small thickness. The image contrast of the lamellar Line/Space
pattern at such small layer thickness is a new challenge for optical inspection tools. In this investigation, the focus is on the capability for optical inspection systems to capture DSA unique defects such as dislocations and disclination clusters over the system and wafer noise. The study is also extended to investigate wafer level data at multiple process steps and determining contribution from each process step and materials using ‘Defect Source Analysis’ methodology. The added defect pareto and spatial distributions of added defects at each process step are discussed.

As directed self-assembly (DSA) has gained momentum over the past few years, questions about its application to high
volume manufacturing have arisen. One of the major concerns is about the fundamental limits of defectivity that can be attained with the technology. If DSA applications demonstrate defectivity that rivals of traditional lithographic
technologies, the pathway to the cost benefits of the technology creates a very compelling case for its large scale
implementation. To address this critical question, our team at IMEC has established a process monitor flow to track the
defectivity behaviors of an exemplary chemo-epitaxy application for printing line/space patterns. Through establishing
this baseline, we have been able to understand both traditional lithographic defect sources in new materials as well as
new classes of assembly defects associated with DSA technology. Moreover, we have explored new materials and
processing to lower the level of the defectivity baseline. The robustness of the material sets and process is investigated
as well. In this paper, we will report the understandings learned from the IMEC DSA process monitor flow.

Directed Self Assembly (DSA) using block copolymers (BCP) has received considerable attention over the past few
years as a potential complementary lithographic technique. While many are focused on adapting DSA integrations to
high volume manufacturing, the key to the technology’s success lies in its ability to generate low defect patterns. The
best way to drive the technology toward a zero defect solution is to understand the fundamentals of the block copolymer
assembly, the interactions of the block copolymer with the underlying chemical pattern, and the evaluation of process
parameters to obtain a high degree of order of the BCP morphologies. To this end, recent research has investigated
numerous material, structural, and process sensitivities of an exemplary chemo-epitaxy line/space integration. Using the
DSA flow implemented at imec, substrate properties, such as the geometry and chemistry, were studied and provided the
first results regarding the dimensions of the nano-patterns and the energetic conditions necessary to obtain good
alignment of the BCP. Additional parameters that have been explored include BCP film thickness and the bake
conditions used to execute various steps of the flow. With this work, the key parameters that drive the assembly process
have been identified. This will allow the definition of an optimized process window and materials for defect
minimization.

Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse. Such platforms should mimic a typical CAR, containing-apart from the polymer-additional components such as photo acid generators (PAGs) and base quenchers. Here, 193 nm and extreme ultraviolet lithography open-source platforms are presented wherein the chemistry, composition, and concentration are all disclosed. With the aim of fundamentally understand how resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the concentration of both PAG and base quencher were varied. These sets of resists were exposed using high-end optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a function of the exposure wavelength, chemistry, and component concentrations.

The optimization of a grapho-epitaxy process flow for lamellar phase block copolymer frequency multiplication on full 300 mm wafers is discussed. The process uses a dedicated photoresist that, after hardening, allows direct coating and annealing of the block copolymer over it. Some of the critical parameters for optimization of this process were found to be the selection of the neutral layer material and reduction of the prepattern resist height. Process window analysis was done by determining the best dose and focus settings for generating high quality directed self-assembly structures with the prepattern process. A very small process window for good self-assembly and an offset in the optimum dose and focus settings for these two stages of the process were found. Finally, the sensitivity of the process to programmed prepattern imperfections was studied. Programmed protrusions in the prepattern as small as 6 nm were found to cause self-assembly defects.

The implementation of our previously reported chemo-epitaxy method for directed self-assembly (DSA) of block copolymers (BCPs) on 300-mm wafers is described in detail. Some challenges to be addressed include edge bead removal control of the layers forming the exposure stack and uniformity of the deposited films across the wafer. With the fine tuning of the process conditions, this flow provides chemically nanopatterned substrates with well-defined geometry and chemistry. After a film of BCP is annealed on the chemical patterns, high degrees of perfection are achieved. A BCP with natural periodicity of 25 nm was assembled on100-nm pitch prepatterns, obtaining 4X feature multiplication. Top-down scanning electron microscope images show a wide process window with depth of focus >200 nm and exposure latitude >40% for lines and spaces of 12.5-nm half-pitch. We provide a platform for future study of the origin of DSA generated defects and their relationship to process conditions and materials that are amenable to use by the semiconductor industry.

As feature sizes continue to shrink, the discrete nature of light and matter is becoming a significant contributor for the
variations observed in lithography in general and for EUVL in particular. Owing to the 15x higher energy of EUV
compared to ArF photons and similar, if not lower, exposure doses, the number of photons per unit area in EUV is
significantly reduced. If the number of photons per contact hole is considered, the situation is even more dramatic, as the
target area of a contact is smaller for EUVL than for ArF patterning. The latter argument, however, is less of a concern
in the case where the contact hole is fabricated by a negative tone rather than a positive tone process. Since photon shot
noise scales with 1/√(#photons), shot noise statistics would favor a brightfield negative tone over a darkfield positive
tone process. Indeed, stochastic simulations predict an increase in the number of photons used to delineate a 22nm
contact hole structure when printed in EUV using a negative tone instead of a positive tone process. In this paper, we
will quantitatively investigate the stochastic nature of the discreet steps in the lithography process and compare the local
CDU performance of contact holes for both negative and positive tone processes.

Extreme UV lithography or EUVL is still the primary candidate to allow scaling below the 22 nm technological node.
Three major engineering challenges need to be simultaneously solved for a smooth introduction of EUVL into high
volume manufacturing: source power and reliability, mask readiness, and photoresist performance. For the EUV reticle
infrastructure, most of the emphasis to date has been put on obtaining and maintaining a low number of mask defects.
However, the reticle flatness requirements for EUV masks are also very stringent. Recent theoretical studies have
indicated that multilayer roughness higher than 50 pm causes line edge roughness. In this paper we engineered an EUV
mask having a systematic surface roughness aggravation. We exposed this mask on the IMEC ASML NXE:3100,
equipped with an USHIO/XTREME discharge-produced plasma (DPP) source. Herein, we present the experimental
results illustrating the impact of mask surface roughness on 27 nm half-pitch lines/spaces. No evidence of aggravated
line edge roughness was found on the wafer when the mask surface roughness was lower than 500 pm.

Directed Self-Assembly (DSA) of block copolymers is considered to be a potential lithographic solution to achieve
higher feature densities than can be obtained by current lithographic techniques. However, it is still not well-established
how amenable DSA of block copolymers is to an industrial fabrication environment in terms of defectivity and
processing conditions. Beyond production-related challenges, precise manipulation of the geometrical and chemical
properties over the substrate is essential to achieve high pattern fidelity upon the self-assembly process. Using our
chemo-epitaxy DSA approach offers control over the surface properties of the slightly preferential brush material as well
as those of the guiding structures. This allows for a detailed assessment of the critical material parameters for defect
reduction. The precise control of environment afforded by industrial equipment allows for the selective analysis of
material and process related boundary conditions and assessment of their effect on defect generation.
In this study, the previously reported implementation of our feature multiplication process was used to investigate the
origin of defects in terms of the geometry of the initial pre-patterns. Additionally, programmed defects were used to
investigate the ability of the BCP to heal defects in the resist patterns and will aid to assess the capture capability of the
inspection tool. Finally, the set-up of the infrastructure that will allow the study the generation of defects due to the
interaction of the BCP with the boundary conditions has been accomplished at imec.

One of the main challenges for developing EUV resists is to satisfy sidewall roughness to allowable limit. With
concern of this challenge, in this paper we study the effects of PAG and sensitizer concentration on the CD variation
and roughness of contact holes in a EUV resist for a range of exposure doses by applying an advanced
characterization methodology. It is found that the contact edge roughness(CER) parameters(RMS,ξ) merge when
they are plotted versus the final CD value revealing the critical role of contact CD in the dependence of CER on
PAG and sensitizer. This finding means that for specific target CD, different PAG and sensitizer concentrations
modify only slightly contact edge roughness parameters. Power spectrum analysis reveals the importance of low
frequency edge undulations in RMS dependence on CD. In addition, we found that CD Variation increase with
sensitizer concentration.

Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm
wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely
understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject
is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source
photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse.
Such platforms should mimic a typical CAR, containing - apart from the polymer - additional components such as photo
acid generators (PAGs) and base quenchers. In this paper, 193 nm and EUVL open-source platforms are presented
wherein the chemistry, composition, and concentration are all disclosed. With the aim to fundamentally understand how
resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the
concentration of both PAG and base quencher were varied. These sets of resists were exposed using both high-end
optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a
function of the exposure wavelength, chemistry, and component concentrations.

As Extreme Ultra Violet technology (EUV) is being introduced, multilayer hard mask patterning becomes a key option
in order to transfer the lithographic patterns into the circuit stack. In particular, spin-on multilayers can play a decisive
role on the process roadmap as a more cost-effective solution than Chemical Vapour Deposition options. The integration
of spin-on hard masks in EUV technology nevertheless requires these products to be EUV-outgassing friendly. In
addition to this, the spin-on solutions must withstand the demanding photoresist and circuit stack aspect ratios during
patterning. This paper presents the EUV process development for contacted metal lines with 30nm half-pitch dimensions
in a dual damascene application. The performance of an all-spin-on multilayer system composed of an EUVphotosensitive
layer, an organic underlayer, a silicon-rich middle layer and a carbon-rich bottom layer is demonstrated.
Firstly, outgassing of the various polymer layers in vacuum is a critical parameter to control since it can directly impact
the EUV-tool-optics lifetime. The qualification, selection and process optimisation of different materials for use in the
ASML NXE:3100 EUV scanner are shown by interpreting Residual Gas Analysis data. The outgassed species for
different types of layers are compared. In this study, the shielding effect of the top layers on the outgassing of the layers
underneath is quantified. The influence of the layer composition is also discussed.
Secondly, the lithographic performance of the 30nm half-pitch process on the NXE:3100 is characterized with process
windows and profile control using the IMEC process-of-reference. The CD uniformity results within wafer and across
wafer-batches are used to demonstrate the process maturity.
Finally, considering the patternability of the EUV process, we demonstrate the ability of the all-spin-on multilayer
system to planarize over the challenging dual damascene topography. To conclude on the potential of this scheme, we
describe the etched dual damascene patterns into a dielectric stack which is representative for the 30nm half pitch
technology node.

We have investigated a H2 plasma smoothing process that improves the Line-Width-Roughness (LWR) and Line-Edge-
Roughness (LER) of the EUV PR at 30 nm half pitch. This process reduces the LWR from ~5.8 to ~3.7 nm, a ~30%
improvement. The main responsible for improving the LER/LWR under H2 plasma seems to be the vacuum ultraviolet
light (VUV) below 120 nm together with the low energy hydrogen ions and radicals. The Fourier transform infrared
(FTIR), X-ray photoelectron spectroscopy (XPS) and liquid proton nuclear magnetic resonance (NMR) analyses suggest
a depletion of oxygen containing groups and reduction of the aromatic groups in the PR. XPS revealed that the PR
surface is rapidly modified by the H2 plasma compared with the bulk (FTIR). Thus a cross-linked top surface is created
which seems to be the limiting step for further LER/LWR improvement.
The main challenge for dry etching is the EUV PR height which after lithography exposure and plasma smoothing, is
less than 40 nm, provoking a low process window for subsequent etching steps. One strategy to open the process window
is to encapsulate the PR with a more resistant material without destroying the lithography pattern. For this purpose a
process was developed where 5-7nm of SiO2-like layer was deposited on top of the PR at low temperature (50 degrees
Celsius). The main advantage of this deposited layer is that it is thicker on the top of the lines than in between them.

Directed Self-Assembly (DSA) is gaining momentum as a means for extending optical lithography past its current limits.
There are many forms of the technology, and it can be used for creating both line/space and hole patterns.1-3 As with any
new technology, adoption of DSA faces several key challenges. These include creation of a new materials infrastructure,
fabrication of new processing hardware, and the development of implementable integrations. Above all else,
determining the lowest possible defect density remains the industry's most critical concern. Over the past year, our
team, working at IMEC, has explored various integrations for making 12-14nm half-pitch line/space arrays. Both
grapho- and chemo-epitaxy implementations have been investigated in order to discern which offers the best path to high
volume manufacturing. This paper will discuss the manufacturing readiness of the various implementations by
comparing the process margin for different DSA processing steps and defect density for the entirety of the flow. As part
of this work, we will describe our method for using programmed defectivity on reticle to elucidate the mechanisms that
drive self-assembly defectivity on wafer.

In the last years, interest in reducing linewidth roughness (LWR) in EUV lithography through a dedicated process step has significantly increased. Various post-litho processing techniques to improve LWR without compromising resolution or sensitivity have been proposed. While these techniques are giving smoothing levels up to 30% before etch, the important question is, of course, how efficient they are in the full patterning process. To evaluate the effectiveness of the smoothing techniques on the EUV resist process and the post-etch pattern, a few of the most promising techniques have been selected for evaluation. Post-develop rinse smoothing and solvent vapor smoothing can reduce the LWR by 10% to 15%. Ion-beam smoothing is giving higher smoothing values, but suffers some important limitations for its application. Two case studies of post-litho smoothing followed by a standard etch process reveal that a large portion of the LWR smoothing can remain after etch, but the LWR gain may also be completely lost. Finally, a plasma smoothing process combined with a layer deposition is proposed to optimize the etch process itself. Analysis of LWR in the spatial frequency domain at the different stages of the patterning process gives a better insight into the impact of the different steps.

In this paper the Arrhenius behavior of blur upon extreme ultraviolet (EUV) exposure is investigated through variation of the post-exposure bake (PEB) temperature. In this way, thermally activated parameters that contribute to blur (such as acid/base diffusion) can be separated from nonthermally activated parameters (such as secondary electron blur). The experimental results are analyzed in detail using multiwavelength resist modeling based on the continuum approach and through fitting of the EUV data using stochastic resist models. The extracted blur kinetics display perfectly linear Arrhenius behavior, indicating that there is no sign for secondary electron blur at 22-nm half pitch. At the lowest PEB setting the total blur length is ∼4 nm, indicating that secondary electron blur should be well below that. The stochastic resist model gives a best fit to the current data set with parameters that result in a maximum probability of acid generation at 2.4 nm from the photon absorption site. Extrapolation of the model predicts that towards the 16-nm half pitch the impact on sizing dose is minimal and an acceptable exposure latitude is achievable. In order to limit the impact on linewidth roughness at these dimensions it will be required to control acid diffusion to ∼5 nm.

In this paper, we present a methodology for the characterization of Contact Edge Roughness (CER) using top-down
SEM images and an algorithm for the generation of model contact edges with controlled roughness as well as
synthesized SEM images with CER. The characterization methodology is applied to the determination of the effects of
exposure dose on the amplitude and frequency parameters of the CER of an EUV resist, while the model edges are used
for understanding the results and connecting RMS to CD variation. Experiments show us that the RMS value of CER
decreases as dose decreases contrary to what happens to LER/LWR. Modeling shows that RMS decreases and CD
variation increases as the sampled edge length is decreased, in agreement with LER/LWR. Thus, modelling may offer an
explanation of the RMS reduction with reduced dose: Indeed, decrease of dose causes reduction of Critical Dimension
(CD) (i.e. diameter) of the hole and therefore reduction of its circumference (i.e. measurement edge length), which in
turn causes reduction of RMS and increase in CD variation.

EUV lithography is expected to be the key lithography option for sub-22nm device manufacturing. In order to meet the
required imaging capability, resist performance improvements are being investigated by exploring both chemically
amplified resists (CAR) and non-CAR chemistries. Another critical item related to resist chemistry is the EUV
irradiation induced outgassing and its risk for optics contamination, especially towards high source power (pre-)
productions tools. In this area it is important to characterize for the different chemistries which resist components are
critical for EUV induced outgassing and - more important - which can result in non-cleanable mirror contamination.
In this paper, we will explore the outgassing and contamination behavior of CAR and non-CAR resist by using Residual
Gas Analysis (RGA) for identifying the resist outgassing characteristics, and by Witness Sample (WS) testing to evaluate
the tendency for contamination. For CAR resists, it has been found that the PAG cation is a key component contributing
to the contamination, but its impact can be changed by changing the resist formulation. In this investigation several
model resists have been evaluated in order to understand which chemical components have - or don't have - an impact
on the contamination. This has led to a proposal of a definition for a resist family. For non-CAR materials, the
investigation has focused to a number of example resists. Most results are related to poly(-olefin sulfones), which have
been proven to be good candidate materials for outgassing and contamination learning. The tests have confirmed that
aromatic groups present in resist outgassing are playing an important role. As an opposite example of non-CAR
material, the inorganic Inpria resist was tested, which revealed that its resist outgassing (water and oxygen) can remove
carbon contamination.
The combined work on CAR and non-CAR outgassing and contamination has learned significantly on the relationship
between resist chemistry, its outgassing and contamination, and provided understanding on how to design good
performing EUV resists with minimal risk for optics contamination in EUV device manufacturing.

In the last years, interest in reducing line width roughness (LWR) in EUV lithography through a dedicated process step
has significantly increased. Various post-litho processing techniques to improve LWR without compromising resolution
or sensitivity have been proposed. While these techniques are giving smoothing levels up to 30% before etch, the
important question is of course how efficient they are in the full patterning process.
To evaluate the effectiveness of the smoothing techniques on the EUV resist process and the post-etch pattern, a few of
the most promising techniques have been selected for an evaluation. Post-develop rinse smoothing and solvent vapor
smoothing can reduce the LWR by 10-15%. Ion-beam smoothing is giving higher smoothing values but suffers some
important limitations for its application.
Two case studies of post-litho smoothing followed by a standard etch process reveal that a large portion of the LWR
smoothing can remain after etch, but the LWR gain may also be completely lost. Finally, a plasma smoothing process
combined with a plasma layer deposition is proposed to optimize the etch process itself. Analysis of LWR in the spatial
frequency domain at the different stages of the patterning process gives a better insight into the impact of the different
steps.

Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice
the pitch of a mask. The proof-of-concept has been published in the previous paper and demonstrated by
others. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line
edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the
LER in this process. Challenges were summarized toward low LER and good performing pitch division.
Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for
pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New
pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on
analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.

Resist line edge/width roughness is one of the most critical aspects in EUV lithography for the 32 nm technological node
and below. It is originated by the uncertainties which characterize the lithographic process: source speckle effect, mask
line and surface roughness, mirror roughness, flare effect and resist pattern formation all contribute to the final
roughness.
In this paper mask and resist line edge roughness were compared by means of frequency analysis on top-down SEM
images: it was found that low frequencies mask roughness are well correlated with the Power Spectral Density of the
resist roughness. Mask high frequencies components resulted less critical due to the natural cut-off of the optical system.
Experimental data for both mask and resist were implemented in the PROLITH Stochastic Resist Model simulator to
quantify the mask line edge roughness contribution to the final resist roughness: the results showed that 16% of the low
frequency resist roughness component is originated at the mask level. For that reason, mask impact was set as 0.6 nm of
the overall line edge roughness resist budget.

In order to further understand the processing sensitivities of the EUV resist process, TEL and imec have continued their
collaborative efforts. For this work, TEL has delivered and installed the state of the art, CLEAN TRACK™ LITHIUS
Pro™ -EUV coater/developer to the newly expanded imec 300mm cleanroom in Leuven, Belgium. The exposures
detailed in this investigation were performed off-line to the ASML EUV Alpha Demo Tool (ADT) as well as on the inline
ADT cluster with CLEAN TRACK™ ACT™ 12 coater/developer. As EUV feature sizes are reduced, is it apparent
that there is a need for more precise processing control, as can be demonstrated in the LITHIUS Pro™ -EUV. In
previous work from this collaboration1, initial investigations from the ACT™ 12 work showed reasonable results;
however, certainly hardware and processing improvements are necessary for manufacturing quality processing
performance. This work continues the investigation into CDU and defectivity performance, as well as improvements to
the process with novel techniques such as advanced defect reduction (ADR), pattern collapse mitigation with FIRM™Extreme and resolution improvement with tetrabutylammoniumhydroxide (TBAH).

EUV lithography is the most promising new technology for the next node of semiconductor devices. Unfortunately, the
high energy photons are likely to generate more contamination than observed with ArF or KrF light which can reduce the
transmission of the EUV optics. Resist outgassing is considered to be an important contamination source, however, not
enough is known about the way a resist composition influences the contamination growth rate, while this information is
crucial to guide the development of EUV resists.
To reduce the knowledge gap, FUJIFILM and imec started a joint effort aimed at systematically exploring the
contribution of the different resist components and at understanding the effect of chemical modifications of the different
components on the contamination tendency of resists. The project focuses on (1) the identification and quantification of
the outgassing components from resist by RGA measurements, (2) on the quantification of the resist related
contamination rate by witness sample (WS) testing, and (3) on the correlation between these two results knowing the
details of the resist chemistry.
To explore the effect of the resist composition upon contamination growth, the following approach was followed. The
focus was put on chemically amplified resists (CAR), since this chemistry is mostly used in EUV lithography. Both
PAG blended as well as PAG bound systems were explored, and the following resist components are individually varied:
polymer matrix, blocking groups, PAG type and concentration. In this way the total contamination of a resist can be
divided into the separate contributions of the different resist components upon the contamination growth rate, which is a
huge step forward in the understanding of optics contamination due to resist.

In this work we present insights into RLS trade-offs by combining experimental data mining and resist modeling and
simulation techniques with a development rate monitor (DRM). A DRM provides experimentally-determined
dissolution characteristics for a given resist process and potentially can be used to produce a more accurate model
description of the process. This work presents experimentally-determined dissolution characteristics for ultra-thin
(50nm) EUV resist films as a function of material type and developer conditions and their impact to RLS trade-offs.
Resist models are created with DRM data for its dissolution characteristics and used in subsequent simulations to gain
fundamental understanding of EUV lithographic performance. In addition to typical lithographic quality metrics
(exposure latitude, DOF), the interaction of resist properties (ie, de-protection kinetics and dissolution) with processing
techniques are also discussed. Finally, a description of the RLS trade-off with respect to resist properties and process
conditions is discussed.

Resist line-edge/width roughness is one of the most critical aspects in extreme UV lithography for the 32-nm technological node and below. It is originated by the uncertainties which characterize the lithographic process: source speckle effect, mask line and surface roughness, mirror roughness, flare effect, and resist pattern formation all contribute to the final roughness. In this paper mask and resist line-edge roughness were compared by means of frequency analysis on top-down scanning electron microscopy images: it was found that low frequency mask roughness is well correlated with the power spectral density of the resist roughness. Mask high-frequency components resulted less critical due to the natural cut-off of the optical system. Experimental data for both mask and resist were implemented in the PROLITH stochastic resist model simulator to quantify the mask line edge roughness contribution to the final resist roughness: the results showed that, for the particular lithographic setting used during the exposures, 16% of the low frequency resist roughness component is originated at the mask level. For this reason, mask impact was set as 0.6 nm of the overall line edge roughness resist budget.

In this paper the Arrhenius behavior of blur upon EUV exposure is investigated through variation of the PEB
temperature. In this way, thermally activated parameters that contribute to blur (such as acid/base diffusion) can be
separated from non-thermally activated parameters (such as secondary electron blur). The experimental results are
analyzed in detail using multi-wavelength resist modeling based on the continuum approach and through fitting of the
EUV data using stochastic resist models. The extracted blur kinetics display perfectly linear Arrhenius behavior,
indicating that there is no sign for secondary electron blur at 22nm half pitch. At the lowest PEB setting the total blur
length is ~4nm, indicating that secondary electron blur should be well below that. The stochastic resist model gives a
best fit to the current data set with parameters that result in a maximum probability of acid generation at 2.4nm from the
photon absorption site. Extrapolation of the model predicts that towards the 16nm half pitch the impact on sizing dose is
minimal and an acceptable exposure latitude is achievable. In order to limit the impact on line width roughness at these
dimensions it will be required to control acid diffusion to ~5nm.

The goal of this work is to use a combination of experiment and calibrated resist models to understand the impact of photo-acid generator (PAG) and sensitizer loading on the performance of a polymer bound PAG resist based processes for extreme ultraviolet (EUV) lithography. This paper describes construction of a chemically amplified resist model across 248 nm, 193 nm, and EUV imaging wavelengths. Using resist absorbance input as obtained from experiment and modeling, only the acid formation kinetics are allowed to vary across imaging wavelengths. This constraining system affords very good fitting results, which provides high confidence that the extracted parameters from the model have actual physical significance. The quantum efficiency for acid formation in EUV is found to be ∼8× higher than at 248 or 193 nm, due to the excitation mechanism by secondary electrons. Most notably for the polymer bound PAG system under study the model provides an extremely low acid diffusion length (∼8 nm), suggesting an excellent inherent resolution for this material. Next, resist models are created for a series of sensitizer containing polymer bound PAG formulations, where the sensitizer loading is systematically varied. Compared to the reference polymer bound PAG resist without sensitizer the efficiency of acid formation is significantly increased, without a negative impact on either resolution or linewidth roughness. For these materials the quantum efficiency of acid formation in EUV is found to be ∼12× higher than at 248 nm. In these formulations the impact of sensitizer loading on the sizing dose is found to be rather moderate. This may suggest that even at the lowest sensitizer loading studied the energy of the secondary electrons is already efficiently transferred to the PAGs.

A previously developed linewidth roughness analysis technique is used to characterize post-lithography process roughness reduction in the frequency domain. Post-lithography processes are likely to be required to reach the International Technology Roadmap for Semiconductors roughness specifications for the 32-nm and 22-nm technological nodes. The aim of these processes is to reduce 3 linewidth roughness after etch without dramatic changes in critical dimensions. Various techniques are discussed: in-track chemical processes, ion-beam sputtering, and thermal and plasma treatments-each technique manifests a characteristic smoothing, reducing roughness up to 34%. Exploiting roughness mitigation at different frequencies, our target is to determine whether 50% 3 linewidth roughness reduction after etch is feasible.

Roughness of lithographic patterns is typically expressed as the absolute 3σ variation of resist lines by means of edge variation. However, full characterization of the roughness requires both its amplitude and frequency distribution. This necessity arises from the requirement to reduce different roughness frequencies for different lithographic levels. The International Technology Roadmap of Semiconductors (ITRS) has established a dedicated specification for low frequency roughness. To obtain full knowledge of the roughness behavior in the frequency domain, a power spectral density analysis technique is used. It is found that power spectral density has a unique profile for each process. Moreover, the major contribution to the roughness came from the low frequencies range. Besides this, an on-line metrological study on scanning electron microscopy resist roughness repeatability is executed to optimize the capturing image parameters and estimate eventual short- (daily) and long-term (yearly) contributions. In the end, 0.2-nm 3σ line width roughness stability value is found. To verify the validity of analysis and metrology, 32-nm extreme ultraviolet lithography exposures at different flare levels, 45-nm ArF immersion lithography through dose, and a rinse postlithography smoothing process are characterized with the aim to highlight the importance of low frequency roughness detection.

In a 2009 analysis of microbridging defectivity, a design of experiment methodology was used to show the effect of
filtration parameters on microbridging defectivity, specifically focusing on filter retention rating, filter media and design,
filtration rate, and controlled filtration pressure. In that analysis it was shown that different filter architectures provide
the most effective filtration of microbridging and that different filter architectures show different levels of microbridging
defects even when optimally tuned. Ultimately, filter choice and filtration setup matter in removal of microbridging
defects.
In the new analysis, a similar approach was taken with additional filter types. However, in the new study the retention rating of the filters was kept constant at 10nm while other filter parameters were varied, including membrane material and design. This study will show the specific effect of the membrane material and design on microbridging defectivity in addition to the effects of filtration setup.

The reduction of line width roughness (LWR) is a critical issue in developing resist materials for EUV lithography and
LWR represents a trade-off between sensitivity and resolution. Additional post pattern processing is expected as an LWR
reduction technique without impact to resolution or sensitivity. This paper reports the LWR reducing effect of a post-development
resist-smoothing process. Approximately 20% improvement in LWR for ArF immersion exposed resist patterns was achieved for two types of resist and two illumination conditions. The LWR after BARC etching in which
resist-smoothing was applied was decreased relative to the case in which smoothing was not applied. Resist-smoothing
process also reduced LWR of an EUV exposure resist pattern by approximately 10%. These results confirm that resistsmoothing
process is robust for different resists and illumination conditions.

In this paper a previously developed Line Width Roughness (LWR) analysis techniques is used to characterize postlitho
process LWR reduction methods in the frequency domain.
Post-litho processes are likely to be required to reach the ITRS 3σLWR target for the 32nm and 22nm half pitch
technological node. The aim of these lithographic processes is to mitigate the roughness of the resist and ultimately the etched patterns without a dramatic change in Critical Dimensions (CD). Various techniques are discussed: in-track
chemical processes, ion beam sputtering, thermal and plasma treatments as dedicated etch-step. Each technique manifests
a characteristic smoothing in the frequency domain reducing the LWR up to 35%. Exploiting LWR reduction at the different frequencies, and combining these techniques, our target is to determine whether 50% overall LWR reduction is feasible.

This paper describes construction of a chemically amplified resist model across 248nm, 193nm and EUV imaging
wavelengths. Using resist absorbance input as obtained from experiment and modeling, only the acid formation kinetics
are allowed to vary across imaging wavelengths. This very constraining system affords very good fitting results, which
provides high confidence that the extracted parameters from the model have actual physical significance. The quantum
efficiency for acid formation in EUV is found to be ~8X higher than at 248 or 193nm, due to the excitation mechanism
by secondary electrons. Most notably for the polymer bound PAG system under study the model provides an extremely
low acid diffusion length (~7nm), suggesting an excellent inherent resolution for this material.
Next, resist models are created for a series of sensitizer containing polymer bound PAG formulations, where the
sensitizer loading is systematically varied. Compared to the reference polymer bound PAG resist without sensitizer the
efficiency of acid formation is significantly increased, without a negative impact on either resolution or line width
roughness. For the materials the quantum efficiency of acid formation in EUV is found to be ~12X higher than at 248nm.
In these formulations the impact of sensitizer loading on the sizing dose is found to be rather moderate. This may suggest
that even at the lowest sensitizer loading studied the energy of the secondary electrons is already efficiently transferred to the PAGs.

In this paper the contrast behavior of photoresists upon EUV exposure is addressed. During a lithographic exposure, the
intended shape undergoes contrast loss which can be divided into two portions. One part is assigned to exposure tool
induced contrast loss (e.g. aberrations of the exposure optics, mechanical stability of the system), while the other part is
due to chemical processes in the resist during exposure and development. Both contributors have to be decoupled from
each other in order to solely analyze the resist contrast loss. The method presented here is based on an experimental
evaluation of dense line/space patterns obtained from EUV exposures. For decoupling of the resist induced contrast loss
from the exposure tool contrast, the aerial image has to be determined. As an alternative EUV exposure tool the EUV
interference lithography (EUV-IL) beamline at Paul Scherrer Institute is applied for resist qualification. The theoretical
description of the sinusoidal aerial image of the EUV-IL tool is presented as well as the experimental method applied to
analyze resist patterns in terms of resist contrast. Finally, the results are compared with data obtained from ASML's ADT EUV scanner.

Outgassing of photoresist material and the related risk for optics contamination in extreme ultraviolet (EUV) exposure
tools are concerns in the development of EUV lithography, especially towards the high volume manufacturing tools. The
characterization however of which resist species are important for the contamination, and their quantification, is still very
challenging. Currently various techniques are explored worldwide, but there is still no full consensus on which technique
is most adequate. On one hand, investigation is done by measuring only the resist outgassing by residual gas analysis
(RGA), pressure rise or other related analysis techniques. Another investigation approach is focusing on the
measurement of EUV optics contamination by analyzing the contamination generated on a witness sample which is
exposed in the vicinity of resist outgassing.
In this paper, we have focused mainly on the witness sample approach as a possible candidate for photoresist
qualification. Contamination results obtained at ASML's and imec's test equipment are compared, which enables better
understanding of the parameters that can affect the resist related contamination growth. Moreover, the contamination
generated on the witness samples is characterized in detail towards thickness as well as composition, by using various
material analysis techniques. Finally the contamination behavior is compared to the RGA resist outgassing information
for better understanding of the over-all issue. These findings form a solid basis to quantify the risks involved of using specific photoresist materials in high volume manufacturing exposure tools with a simple but adequate test method, applied to qualify resists.

Dual-tone development (DTD) has been previously proposed as a potential cost-effective double patterning technique1.
DTD was reported as early as in the late 1990's2. The basic principle of dual-tone imaging involves processing exposed
resist latent images in both positive tone (aqueous base) and negative tone (organic solvent) developers. Conceptually,
DTD has attractive cost benefits since it enables pitch doubling without the need for multiple etch steps of patterned
resist layers. While the concept for DTD technique is simple to understand, there are many challenges that must be
overcome and understood in order to make it a manufacturing solution.
Previous work by the authors demonstrated feasibility of DTD imaging for 50nm half-pitch features at 0.80NA (k1 =
0.21) and discussed challenges lying ahead for printing sub-40nm half-pitch features with DTD. While previous
experimental results suggested that clever processing on the wafer track can be used to enable DTD beyond 50nm halfpitch,
it also suggest that identifying suitable resist materials or chemistries is essential for achieving successful imaging
results with novel resist processing methods on the wafer track. In this work, we present recent advances in the search
for resist materials that work in conjunction with novel resist processing methods on the wafer track to enable DTD.
Recent experimental results with new resist chemistries, specifically designed for DTD, are presented in this work. We
also present simulation studies that help and support identifying resist properties that could enable DTD imaging, which
ultimately lead to producing viable DTD resist materials.

In an effort to improve on the sensitivity of commercial nonchemically amplified e-beam resists, four polyacrylates functionalized with -CF3 and/or CH2CF3 alkoxy substituents were studied. The -CF3 substituent is known to increase backbone-scission efficiency while simultaneously eliminating acidic outgassing and cross-linking known to occur in -halogen substituted polyacrylates. Contrast curves for the polymeric -CF3 acrylates, generated through e-beam exposure, showed that the resists required an order of magnitude less dose than the current industry standards, poly(methyl methacrylate) (PMMA) and ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via 60Co -ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of poly(methyl -trifluoromethacrylate) (PMTFMA) was found to be 2.8× and 4.0× faster, respectively, than PMMA.

The challenge in obtaining good resist performance in terms of resolution, line width roughness and sensitivity at EUV
wavelength forces to make more efficient use of photons that reach the wafer plane than has been the case for traditional
optical lithography. Theory demonstrates that the current absorbance levels of EUV resists are quite far from optimal and
absorbance should be increased. The most attractive pathway to achieve this is by increasing the fluorine content of EUV
resists. The viability of this approach has been demonstrated using non-chemically amplified PMMA as model resist and
comparing its photospeed with a fluorinated analogue. It has been demonstrated that the photospeed increases due to
improved resist absorbance by ~1.5X, which is close to 1.7X that is predicted by the difference in absorbance.
Further modeling studies support the experimental results and indicate an optimum for total film absorbance of ~0.20-
0.25. Compared to current platforms this would correspond to an increase in photospeed by ~1.7X which is accompanied with an improvement in LWR of ~1.14X. Combining this approach with the trends in EUV resists to increase PAG loading and include sensitizer in order to improve photospeed will likely provide a path for EUV resists that will meet the specifications that are required for the 32nm and 22nm node.

In an effort to improve upon the sensitivity of commercial non-chemically amplified e-beam resists, four polyacrylates
functionalized with α-CF3 and/or CH2CF3 alkoxy substituents were studied. The α-CF3 substituent is known to increase
backbone-scission efficiency while simultaneously eliminating acidic out-gassing and cross-linking known to occur in α-
halogen substituted polyacrylates. Contrast curves for the polymeric α-CF3 acrylates, generated through e-beam
exposure, showed the resists required an order of magnitude less dose than the current industry-standards, PMMA and
ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via 60Co γ-ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight
demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable
G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of PMTFMA was found to be 2.8x
and 4.0x faster, respectively, than PMMA.

Requirements of resist modeling strategies for EUV and low-k1 ArF nanolithography continue to become
more stringent. Resist designers are consistently faced with the task of reducing exposure dose and line
roughness while simultaneously improving exposure latitude, depth-of-focus and ultimate resolution.
In this work, we briefly discuss a next-generation resist model for the prediction of statistical resist
responses such as line-edge roughness, line-width roughness and CD variability, as well as base
lithographic responses such as exposure latitude. The model's parameterized fit to experimental data from a
state-of-the art polymer-bound PAG resist irradiated at ArF and EUV will be shown. The probabilistic
computation of acid generation at ArF and EUV will be discussed. The factors influencing the
hypothesized primary cause of resist roughness, acid shot noise, are discussed.

High NA immersion and EUV lithography processes are challenged to meet stringent control requirements for the 22 nm
node and beyond. Lithography processes must balance resolution, LWR and sensitivity (RLS) performance tradeoffs
while scaling resist thickness to 100 nm and below. Hardware modules including coat, bake and development seek to
enable resist processes to balance RLS limitations. The focus of this paper is to study the fundamentals of the RLS
performance tradeoffs through a combination of calibrated resist simulations and experiments.
This work seeks to extend the RLS learning through the creation of calibrated resist models that capture the exposure
kinetics, acid diffusion properties, deprotection kinetics and dissolution response as a function of PAG loading in a 193
nm polymer system. The calibrated resist models are used to quantify the resolution and sensitivity performance
tradeoffs as well as the degradation of resist contrast relative to image contrast at small dimensions.
Calibrated resist simulations are capable of quantifying resolution and sensitivity tradeoffs, but lack the ability to model
LWR. LWR is challenging to simulate (lattice models) and to measure; due to the dependence on spectral frequency.
This paper seeks to use micro-bridging experiments as means to better understand the statistical nature of LWR. Microbridging
analysis produces a statistical distribution of "discrete bridging events" that encompasses practical variations
across scanner, track and resist. Micro-bridging and LWR experiments are done using a 1.2 NA immersion system on 45
nm space structures (90 nm pitch) as a means to demonstrate the concept, but the methodology can also be used to study
EUVL processes as the technology matures. The understanding of the RLS performance tradeoffs enables TEL to
develop future hardware and processes that support industry scaling goals.

Microbridging defects have emerged as one of the top yield detractor in semiconductor manufacturing as Moore's law
drives towards 32nm processing utilizing immersion lithography. It is generally recognized that there are multiple root
causes for microbridging defectivity. Image and resist contrast and different developer techniques have been studied and
their contribution to microbridging defectivity has been described. In this study we will focus on the effect of point-ofuse
filtration and how it is best used to mitigate microbridging defectivity.
A design of experiment methodology will be utilized to understand the effect of various filter and filtration parameters
on microbridging defectivity, including filter retention rating, filter media and design, filtration rate, and controlled
filtration pressure. It is anticipated that by better understanding the effect of point-of-use filtration on microbridging
defectivity, guidelines for better control of this type of defect may be formulated.

Extreme ultraviolet interference lithography (EUV IL), especially in combination with tool-independent metrics for resist performance, is a powerful technique for judging progress with current resists, the potential of new materials and studying the fundamentals of resist performance. We provide an overview of how EUV IL is applied for resist testing and early material selections. Also discussed are examples of EUV IL being used to gain fundamental understanding for resist characterization under EUV imaging conditions.

Photoresist outgassing and the related risk for optics contamination in extreme ultraviolet (EUV) exposure tools are
concerns in the development of EUV lithography, especially towards the high volume manufacturing tools. The
measurement however of how much and what species are outgassing/contaminating, is still very challenging. Various
techniques are investigated worldwide, but there is still no consensus on which technique is most adequate. Moreover,
since the outgassing/contamination qualification of photoresists needs dedicated tool set-up, it is likely that the testing
configuration (with parameters such as exposure intensity, background vacuum quality, pumping speed, ...) can impact
the measurement result.
In this paper, we are comparing two candidates for outgassing/contamination measurement which are integrated in one
experimental set-up : RGA (Residual Gas Analysis) and witness plate testing. RGA is based on in situ mass
spectrometer measurements during photoresist EUV exposure and enables chemical identification of species that are
outgassing, but has limited information on the probability of mirror contamination. Results are shown on how the
measurement results can depend on the testing configuration. Witness plate testing is based on the evaluation of EUV
exposed mirror samples that are placed in the vicinity of EUV outgassing photoresist. Results are shown on how the
generated contamination can be affected by the tool configuration, and on how to measure/analyze the contamination.
Finally, since both techniques are integrated in one test-set-up, measurement results will be compared and correlated,
which should help in understanding the phenomena and lead to well defined measurement for photoresist qualification.

The ever-shrinking circuit device dimensions challenge lithographers to explore viable patterning for the 32 nm halfpitch
node and beyond. Significant improvements in immersion lithography have allowed extension of optical
lithography down to 45 nm node and likely into early 32 nm node development. In the absence of single-exposure
patterning solutions, double patterning techniques are likely to extend immersion lithography for 32 nm node
manufacturing. While several double patterning techniques have been proposed as viable manufacturing solutions, cost,
along with technical capability, will dictate which candidate is adopted by the industry.
Dual-tone development (DTD) has been proposed as a potential cost-effective double patterning technique.1 Dual-tone
development was reported as early as in the late 1990's by Asano.2 The basic principle of dual-tone imaging involves
processing exposed resist latent images in both positive tone (aqueous base) and negative tone (organic solvent)
developers. Conceptually, DTD has attractive cost benefits since it enables pitch doubling without the need for multiple
etch steps of patterned resist layers. While the concept for DTD technique is simple to understand, there are many
challenges that must be overcome and understood in order to make it a manufacturing solution.
This work presents recent advances and challenges associated with DTD. Experimental results in conjunction with
simulations are used to understand and advance learning for DTD. Experimental results suggest that clever processing
on the wafer track can be used to enable DTD beyond 45 nm half-pitch dimensions for a given resist process. Recent
experimental results also show that DTD is capable of printing <0.25 k1-factor features with an ArF immersion scanner.
Simulation results showing co-optimization of process variables, illumination conditions, and mask properties are
presented.

The objective of this work is to understand, from a simulation perspective, how current EUV resist chemistries compare to mature 193nm (ArF) photoresist systems. Accurate resist models for EUV resists may be developed using the same in-house calibration methodology used for ArF resists. Using this methodology, key resist properties, such as optical density, dissolution behavior, and imaging characteristics, are correlated to model parameters that have a significant impact on resist imaging performance. Such resist models, once calibrated, are used to make predictions of key lithographic metrics, such as MEF and process latitude. In this work, model calibration results for ArF and EUV resist systems are compared and the resulting resist models are used to contrast fundamental resist behavior at the ArF and EUV wavelengths.

The use of a single figure of merit to judge resist performance
with respect to resolution, linewidth roughness LWR, and sensitivity is
proposed and evaluated. Chemically amplified photoresists used in advanced
lithography nodes need to fulfill stringent requirements for a considerable
number of resist and process characteristics. Along with resolution,
linewidth roughness and resist sensitivity are important examples
where the specifications have become very tight. Previously, it has been
shown that resolution, linewidth roughness, and resist sensitivity are fundamentally
interdependent. Hence, when evaluating or optimizing resist
performance, it is very important to take these three characteristics into
consideration simultaneously. We propose to combine these characteristics
into a single photoresist figure of merit KLUP. This figure of merit,
which is determined from sizing dose, imaging wavelength, resist thickness,
exposure latitude, acid diffusion length, linewidth roughness, and
pitch, allows for a direct comparison of very different resist formulations
independent of the exposure tool used. Thus, KLUP has great potential to
assist in evaluating resist performance for the next lithography nodes, for
both ArF and for EUV wavelengths.

Double patterning is used to scale designs below k1 factors that can be obtained with single patterning. Because of the
double litho and etch steps, however, this is an expensive and time consuming technique. Spacer defined double
patterning, which is commonly used to shrink regular dense patterns as used in memory applications, is an expensive
technique because of the many deposition and etch steps that are required. In this paper, we propose several alternative
process flows which can reduce the cost-of-ownership by eliminating the intermediate etch step in a double litho, double
etch for line/space patterns, and replace it by a process step in the track only. These alternative process flows use thermal
freezing resist, positive/negative resist and coating a freezing material. For these materials 32nm node logic patterning
can be demonstrated, and even 32nm half pitch can be patterned already with one technique. As alternative technique to
spacer defined double patterning, dual tone development is proposed, which can generate pitch doubling in resist using a
single exposure. Proof-of-concept of this technique is shown experimentally.

The fundamental understanding of photo acid generator (PAG) leaching and water uptake is important for the design of
robust immersion imaging processes; including resist, scanner and track hardware design. Experimental studies show
that PAG leaching occurs over a very short time scale (< 10 seconds). Time-of-flight secondary ion mass spectrometry
(TOF-SIMS) analysis also reveals that PAG leaching occurs at the top surface of a resist film. The time scale and depth
of PAG leaching is important to understanding the fundamental impact of immersion process steps on imaging
performance.
Finite element modeling is used to study the diffusion of water into a resist and the diffusion of PAG out of a resist into
flowing water. Experimental mass uptake of water in a 150 nm resist film was collected experimentally using a quartz
crystal microbalance (QCM). The diffusion coefficient of water in the thin resist is calculated to be 1.5e-11 cm2/s. PAG
leaching data was collected from an experimental apparatus that can flow water over a resist coated 200 mm wafer
(dynamic WEXA2). The PAG diffusion model shows that the diffusion coefficient transitions from 1.4 e-14 cm2/s in the
surface of the film to 1.0 e-16 cm2/s in the bulk of the film. The finite element simulations show an excellent physical
correlation to the experimental PAG leaching data.
The extraction of resist component diffusion coefficients enables the modeling of component depth profiles in thin resist
materials. The component depth profile information is then used to model the impact of resist design and immersion
resist processing on 32 nm node imaging performance.

As the industry extends immersion lithography to the 32 nm node, the limits of image and resist contrast will be
challenged. Image contrast is limited by the inherent numerical aperture of a water based immersion lithography system.
Elements of resist design and processing can further degrade the final deprotected image contrast1,2. Studies have been
done to understand the effects of image contrast on line width roughness (LER) for dry 193 nm lithography3. This paper
focuses on the impacts of image and resist contrast on the formation of defects and LER in an immersion lithography
process.
Optical and resist simulations are combined with experiments to better understand the relationship between image
quality, resist design, scanner/track processing and defect formation. The goal of this work is to develop a relationship
between resist contrast metrics and defect formation for immersion processes.

There still remain three major technological lithography options for high volume manufacturing at the 32nm half pitch
node: 193nm immersion lithography with high index materials, enabling NA>1.6; 193nm double patterning and EUV
lithography. In this paper the pros and cons of these three options will be discussed. Particular interest will be paid to the
consequences of the final choice on the resist technology.
High index 193nm immersion lithography also requires high index resist materials, which are under development but
still far removed from the target refractive index and absorbance specifications not to mention lithographical
performance.
For double patterning the pitch may be relaxed, but the resists still need to be able to print very narrow lines and/or
trenches. Moreover, it would be preferred for the resists to support pattern or image freezing techniques in order to step
away from the litho-etch-litho-etch approach and make double patterning more cost effective.
For EUV the resist materials need to meet very aggressive sensitivity specifications. In itself this is possible, but it is
difficult to simultaneously maintain performance in terms of resolution and line width roughness. A new parameter
(KLUP) for assessing resist performance in terms of these three performance criteria will be introduced.

With immersion lithography approaching the insertion in production, watermarks remain as one of the main concerns for
immersion specific defects. They require special attention because of their size and associated high kill-ratio, and their
increasing occurrence at higher scan speeds. IMEC has been working to understand the underlying mechanism of why
remaining water droplets cause these defects.
This work focuses on water uptake measurements and how this parameter correlates to watermark defectivity.
Ellipsometric Porosimetry (EP) is used to measure the water uptake tendencies of resist and top coat materials and stacks
thereof, and investigate what parameters are affecting it. The influence of material and process parameters and the
presence of a top coat on water uptake by the resist are evaluated. In parallel, the quartz crystal microbalance (QCM)
technique has been used as an alternative option to measure the water uptake. Though a one-to-one comparison between
the results is not straightforward, the main trends are identical for both techniques.
No perfect correlation of watermark defectivity with water uptake has been found in this study. Nevertheless, the results
show a tendency towards higher watermark sensitivity with higher water uptake by the film. It is recognized that the total
watermark defectivity is most probably a complex interplay of different parameters with water uptake being only one of
them.

A series of experiments were designed to probe the interaction between second generation High Index Liquids (HIL,
n=1.65) and the resist stack. Three different second-generation high index liquids were tested in five experiments:
measurement of the contact angle of the liquid with the resist surface; leaching of Photo-Acid Generator (PAG) into the
liquid; residue analysis of droplets evaporated from the resist surface; impact of liquid soaking on resist profiles; and
imaging through high-index liquids at 72nm pitch. The selected liquids were the main candidates from two potential
vendors. In parallel, tests have also been done for water. The tests show that one of the main differences between highindex
liquids and water is their much smaller contact angles on the organic photoresist films. This contact angle can be
influenced by a topcoat, but currently seen contact angles may force a new immersion hood concept. Imaging was not
affected strongly by the high-index liquids. For some liquids, low evaporation rates and a tendency to leave residue on
resist were observed, which may require a dedicated liquid removal strategy to reduce defectivity.

In this paper, the use of a single Figure-of-Merit to judge resist performance with respect to line width roughness, resolution and sizing dose is proposed and evaluated. Chemically amplified photoresists used in advanced lithography nodes need to fulfill stringent requirements for a considerable number of resist and process characteristics. Along with resolution, line width roughness and resist sensitivity are important examples where the specifications have become very tight. Previously, it has been shown that resolution, line width roughness and resist sensitivity are fundamentally interdependent. Hence, when evaluating or optimizing resist performance it is very important to take these three characteristics into consideration simultaneously. We propose to combine these characteristics in a single photoresist Figure of Merit KLUP. This Figure of Merit, which is determined from sizing dose, imaging wavelength, exposure latitude, acid diffusion length, line width roughness and pitch allows for a direct comparison of very different resist formulations independent of the exposure tool used. Thus, KLUP has great potential to assist in evaluating resist performance for the next lithography nodes, for both ArF and for EUV wavelengths.

IMEC has started an EUV lithography research program based on ASMLs EUV full field scanner, the Alpha Demo Tool
(ADT). Currently, the ADT is in the final phase of installation. The program focuses on three main projects: EUV
resists, EUV reticles and assessment of the ADT performance. The intent of this program is to help improve and
establish the necessary mask and resist infrastructure. In this paper, the status and the progress of the program is
reviewed. In preparation for a resist process for the ADT, interference lithography has been used to track the progress of
resist performance. Steady progress in resist development is seen, especially in terms of resolution, as some materials
are now able to resolve 25nm HP. In its initial phase, the reticle project has concentrated on working with the mask and
blank suppliers to assure timely availability of reticles for the ADT. An overview is given of the other reticle related
activities, as well as first results of a defect printability study by simulation. In the ADT assessment project, simulation
studies are reported aimed at the development of optical correction for flare and reticle shadowing effects. The impact of
flare and shadowing effects are well understood and strategies for flare mitigation and shadowing effect correction are
proposed.

Extreme ultraviolet lithography (EUVL) uses a reflective mask with a multilayer coating. Therefore, the illumination is
an off-axis ring field system that is non-telecentric on the mask side. This non-zero angle of incidence combined with the
three-dimensional mask topography results in the so-called "shadowing effect". The shadowing causes the printed CD to
depend on the orientation as well as on the position in the slit and it will significantly influence the image formation [1,2]. In addition, simulations show that the Bossung curves are asymmetrical due to 3-D mask effects and their best focus
depends on the shadowing angle [3]. Such tilts in the Bossung curves are usually associated with aberrations in the
optical system. In this paper, we describe an approach in which both properties can be disentangled.
Bossung curve simulations with varying effective angles of incidence (between 0 and 6 degrees) show that at discrete
defocus offsets, the printed linewidth is independent of the incident angle (and thus independent of the shadowing effect),
the so-called iso-sciatic (constant shadowing) point. For an ideal optical system this means that the size of a
printed feature with a given mask-CD and orientation does not change through slit. With a suitable test structure it is
possible to use this effect to distinguish between mask topography and imaging effects from aberrations through slit.
Simulations for the following aberrations tested the approach: spherical, coma and astigmatism.

Since the moment immersion lithography appeared in the roadmaps of IC manufacturers, the question whether to use top coats has become one of the important topics for discussions. The top coats used in immersion lithography have proved to serve as good protectors from leaching of the resist components (PAGs, bases) into the water. However their application complicates the process and may lead to two side effects. First, top coats can affect the process window and resist profile depending on the material's refractive index, thickness, acidity, chemical interaction with the resist and the soaking time. Second, the top coat application may increase the total amount of defects on the wafer. Having an immersion resist which could work without the top coat would be a preferable solution. Still, it is quite challenging to make such a resist as direct water/resist interaction may also result in process window changes, CD variations, generation of additional defects. We have performed a systematic evaluation of a large number of immersion resist and top coat combinations, using the ASML XT:1250Di scanner at IMEC. The samples for the experiments were provided by all the leading resist and top coat suppliers. Particular attention was paid to how the resist and top coat materials from different vendors interacted with each other. Among the factors which could influence the total amount of defects or CD variations on the wafer were: the material's dynamic contact angle and its interaction with the scanner stage speed, top coat thickness and intermixing layer formation, water uptake and leaching. We have examined the importance of all mentioned factors, using such analytical techniques as Resist Development Analyser (RDA), Quartz Crystal Microbalance (QCM), Mass Spectroscopy (MS) and scatterometry. We have also evaluated the influence of the pre- and pos- exposure rinse processes on the defectivity. In this paper we will present the data on imaging and defectivity performance of the resists with and without the use of top coats. So far we can conclude that top coat/resist approach used in immersion lithography needs some more improvements (i.e. process, materials properties) in order to be implemented in high volume manufacturing.

This paper describes a method to measure the dynamic behavior of resist leaching in the time domain that is relevant for immersion lithography. The total leaching amount as a function of the contact time between water and resist is obtained and successfully fitted using previously described kinetic equations. In this way valuable information is obtained for the understanding of the contribution of resist leaching to lens contamination, CD uniformity and defectivity. The procedure is further used to study the effectiveness of various leaching mitigation strategies. Top coats prove to be a very effective method to reach the leaching specifications of the tool vendors. Also immersion dedicated resist materials meet the specifications or come very close.

Defectivity has been one of the largest unknowns in immersion lithography. It is critical to understand if there are any immersion specific defect modes, and if so, what their underlying mechanisms are. Through this understanding, any identified defect modes can be reduced or eliminated to help advance immersion lithography to high yield manufacturing. Since February 2005, an ASML XT:1250Di immersion scanner has been operational at IMEC. A joint program was established to understand immersion defectivity by bringing together expertise from IMEC, ASML, resist vendors, IC manufactures, TEL, and KLA-Tencor. This paper will cover the results from these efforts. The new immersion specific defect modes that will be discussed are air bubbles in the immersion fluid, water marks, wafer edge film peeling, and particle transport. As part of the effort to understand the parameters that drive these defects, IMEC has also developed novel techniques for characterizing resist leaching and water uptake. The findings of our investigations into each immersion specific defect mechanism and their influencing factors will be given in this paper, and an attempt will be made to provide recommendations for a process space to operate in to limit these defects.

Two-beam interference of 193nm laser light can print dense line-space patterns in photoresist, down to a resolution that can only be obtained using hyper-NA scanners, and allows for early learning on hyper-NA imaging and process development. For this purpose, a dedicated two-beam interference immersion printer, operating at 193nm wavelength, was installed in the IMEC cleanroom. The interference printer consistently generates L/S patterns at 130nm, 90nm, and 72nm pitch with exposure latitudes in the 12-26% range (when using TE-polarized light). At these pitches, process and imaging issues have been studied that are of direct interest for hyper-NA lithography. On the imaging side, we discuss the flexibility of the printer towards working with various polarizations. We show how reflection reduction strategies at the high incidence angles of hyper-NA imaging can be tested in the interference printer. On the processing side, we have screened a number of resists at 90nm pitch. A methodology to study static and dynamic leaching was developed. Several liquids with refractive index >1.6 are currently being developed as potential candidates to replace water for optical lithography at 38nm half-pitch. We have used the interference printer at 72nm pitch, with both water and liquids of refractive index 1.65.

We have investigated the impact of water and top-coats on the resist in water immersion lithography by analyzing the dissolution behavior and the film constitution. We used a resist development analyzer (RDA) and a quartz crystal microbalance (QCM) to study the dissolution behavior. The film constitution was studied through the gradient shaving preparation (GSP) method in combination with TOF-SIMS. The GSP/TOF-SIMS method reveals the constitution of a top-coat/resist film. We found that, in a resist, the photo acid generator (PAG) anion at a depth of about 30 nm from the surface leached into water and a surface insoluble layer formed during immersion. The estimated amount of leaching was about 5% of the original content. The formation of an intermixing layer with a low dissolution rate was observed for some top-coat and resist combinations. The thickness of the intermixing layer and the formation behavior were made clear. We believe the intermixing layer was caused by the top-coat solvent eluting resist components. In a top-coat, a PAG existed within the top-coat and the PAG anion leached into the water. Top-coats blocked gaseous decomposed products from the resist film during PEB. These results are useful for estimating patterning characteristics and the defectivity due to materials for actual immersion exposure.

Most 157nm resist optimization to date has been done with micro-steppers, but there may be significant differences in resist profiles and process windows between micro-steppers and full field scanners. Several resists were evaluated on an ASML MS VII full-field 157nm scanner at IMEC. Focus and exposure latitudes were measured for resist lines using various feature sizes and pitches with different reticle types and illumination conditions. Resist sensitivity to post-expose bake temperature were measured. Delay effects, line-edge roughness, line slimming in a CD SEM, and etch resistance were also evaluated.

This paper presents results of monitoring and control of contaminants in an ASML MS-VII 157nm full-field exposure tool at IMEC, as verified lithographically in terms of field uniformity, lens transmission, CD uniformity, and scattered light. The daily contamination monitoring system utilizes in-line photo-ionization detector, oxygen and moisture analyzers, as well as chemiluminescent detector, and gas chromatograph that is coupled to a mass spectrometer. On a monthly basis, contamination monitoring was performed with thermal desorption-gas chromatographi/mass spectrometric techniques. The following four locations within the optical path of the MS-VII are monitored: source optic assembly, condenser lens optic, 1X relay station, and projection optics box. Contamination control is realized in the system with an on-board purge control unit, which is equipped with gas purifiers that remove contaminants such as H2O, O2, CO, CO2, hydrocarbons, H2, and sulfur compounds. All the observed contaminants have been trending within expected values and no contamination-related tool performance degradation has been observed. The excursions observed in the contaminant concentrations are coincident with tool downtime/maintenance events. Siloxane levels appear to be consistently below 50 ppt in all the monitored locations within the optical path of the tool, except on one occasion when it reached 90 ppt in the projection optics. Volatile organic compounds (VOCs) concentration within the MS-VII enclosure show a stable background level of around 10-25 ppb during weekends and levels of 45-60 ppb (during working days). VOCs concentration variations inside the MS-VII enclosure during the working days correlate well with activities inside the clean room. Air recirculation and low intake of fresh air inside the MS-VII tend to slow down the speed with which the VOCs levels decreases to stable background level, whenever there was a major upward excursion in their concentration. Average light intensity through the projection optics correlates well with oxygen concentration. The average light intensity transmission through the PO lens has shown a steady increase over time due to in-situ laser cleaning with oxygen.

In this paper, a technique for in-line monitoring of acid and base contamination is described. The technique is applied to purge gas monitoring and the air at the in- and outlet of the active charcoal filters on an ASML PAS5500/1100 193nm scanner is analyzed. Unparalleled lower detection limits (LDL) were obtained, especially for acid detection, where LDLs below 10ppt for SOx were achieved. At the inlet high contamination levels (0.5-3ppb) of NO/HONO and SOx are detected. The filters effectively remove the SOx contamination. The residual SOx contamination could be measured and the average was found to be ~2ppt, corresponding to a filtering efficiency of 99.8%. The filtering efficiency for NO and HONO is significantly lower and was found to be ~98%, which is in agreement with previous reports.1

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SC1067: Directed Self Assembly and its Application to Nanoscale Fabrication

This course explains basic principles and applications of directed self assembly (DSA), with particular emphasis on block copolymer directed self assembly. A primary goal of the course is to present in a systematic manner the central issues that govern directed self assembly, and to do so in a way that will enable current and future practicioners of directed self assembly to rapidly identify the potential and limitations of this technique for specific applications. Anyone who wants to answer questions such as, "what structures can I create, how robust are certain processes, or what materials should I employ" will benefit from taking this course.

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